From 19fcec84d8d7d21e796c7624e521b60d28ee21ed Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 20:45:59 +0200 Subject: Adding upstream version 16.2.11+ds. Signed-off-by: Daniel Baumann --- .../tools/auto_index/test/type_traits.docbook | 6673 ++++++++++++++++++++ 1 file changed, 6673 insertions(+) create mode 100644 src/boost/tools/auto_index/test/type_traits.docbook (limited to 'src/boost/tools/auto_index/test/type_traits.docbook') diff --git a/src/boost/tools/auto_index/test/type_traits.docbook b/src/boost/tools/auto_index/test/type_traits.docbook new file mode 100644 index 000000000..64837d71a --- /dev/null +++ b/src/boost/tools/auto_index/test/type_traits.docbook @@ -0,0 +1,6673 @@ + + + + + + + + various authors + + 2000 2006 Adobe Systems Inc, David Abrahams, + Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant, Jesse Jones, Mat + Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten Ottosen, Robert + Ramey and Jeremy Siek + + + Distributed under the Boost Software License, Version 1.0. (See accompanying + file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) + + + Boost.TypeTraits + + A printer-friendly PDF + version of this manual is also available. + +
+ <link linkend="boost_typetraits.intro"> Introduction</link> + + The Boost type-traits library contains a set of very specific traits classes, + each of which encapsulate a single trait from the C++ type system; for example, + is a type a pointer or a reference type? Or does a type have a trivial constructor, + or a const-qualifier? + + + The type-traits classes share a unified design: each class inherits from a + the type true_type + if the type has the specified property and inherits from false_type + otherwise. + + + The type-traits library also contains a set of classes that perform a specific + transformation on a type; for example, they can remove a top-level const or + volatile qualifier from a type. Each class that performs a transformation defines + a single typedef-member type + that is the result of the transformation. + +
+
+ <link linkend="boost_typetraits.background"> Background and Tutorial</link> + + The following is an updated version of the article "C++ Type traits" + by John Maddock and Steve Cleary that appeared in the October 2000 issue of + Dr Dobb's Journal. + + + Generic programming (writing code which works with any data type meeting a + set of requirements) has become the method of choice for providing reusable + code. However, there are times in generic programming when "generic" + just isn't good enough - sometimes the differences between types are too large + for an efficient generic implementation. This is when the traits technique + becomes important - by encapsulating those properties that need to be considered + on a type by type basis inside a traits class, we can minimize the amount of + code that has to differ from one type to another, and maximize the amount of + generic code. + + + + + Foo1 + + Consider an example: when working with character strings, one common operation + is to determine the length of a null terminated string. Clearly it's possible + to write generic code that can do this, but it turns out that there are much + more efficient methods available: for example, the C library functions strlen and wcslen + are usually written in assembler, and with suitable hardware support can be + considerably faster than a generic version written in C++. The authors of the + C++ standard library realized this, and abstracted the properties of char and wchar_t + into the class char_traits. + Generic code that works with character strings can simply use char_traits<>::length to determine the length of a null + terminated string, safe in the knowledge that specializations of char_traits will use the most appropriate + method available to them. + + + + Type Traits + + + Class char_traits is a classic + example of a collection of type specific properties wrapped up in a single + class - what Nathan Myers termed a baggage class[1]. In the Boost type-traits library, + we[2] have written a set of very + specific traits classes, each of which encapsulate a single trait from the + C++ type system; for example, is a type a pointer or a reference type? Or does + a type have a trivial constructor, or a const-qualifier? The type-traits classes + share a unified design: each class inherits from a the type true_type + if the type has the specified property and inherits from false_type + otherwise. As we will show, these classes can be used in generic programming + to determine the properties of a given type and introduce optimizations that + are appropriate for that case. + + + The type-traits library also contains a set of classes that perform a specific + transformation on a type; for example, they can remove a top-level const or + volatile qualifier from a type. Each class that performs a transformation defines + a single typedef-member type + that is the result of the transformation. All of the type-traits classes are + defined inside namespace boost; + for brevity, namespace-qualification is omitted in most of the code samples + given. + + + + Implementation + + + There are far too many separate classes contained in the type-traits library + to give a full implementation here - see the source code in the Boost library + for the full details - however, most of the implementation is fairly repetitive + anyway, so here we will just give you a flavor for how some of the classes + are implemented. Beginning with possibly the simplest class in the library, + is_void<T> inherits + from true_type + only if T is void. + + +template <typename T> +struct is_void : public false_type{}; + +template <> +struct is_void<void> : public true_type{}; + + + Here we define a primary version of the template class is_void, + and provide a full-specialization when T + is void. While full specialization + of a template class is an important technique, sometimes we need a solution + that is halfway between a fully generic solution, and a full specialization. + This is exactly the situation for which the standards committee defined partial + template-class specialization. As an example, consider the class boost::is_pointer<T>: + here we needed a primary version that handles all the cases where T is not + a pointer, and a partial specialization to handle all the cases where T is + a pointer: + + +template <typename T> +struct is_pointer : public false_type{}; + +template <typename T> +struct is_pointer<T*> : public true_type{}; + + + The syntax for partial specialization is somewhat arcane and could easily occupy + an article in its own right; like full specialization, in order to write a + partial specialization for a class, you must first declare the primary template. + The partial specialization contains an extra <...> after the class name + that contains the partial specialization parameters; these define the types + that will bind to that partial specialization rather than the default template. + The rules for what can appear in a partial specialization are somewhat convoluted, + but as a rule of thumb if you can legally write two function overloads of the + form: + + +void foo(T); +void foo(U); + + + Then you can also write a partial specialization of the form: + + +template <typename T> +class c{ /*details*/ }; + +template <typename T> +class c<U>{ /*details*/ }; + + + This rule is by no means foolproof, but it is reasonably simple to remember + and close enough to the actual rule to be useful for everyday use. + + + As a more complex example of partial specialization consider the class remove_extent<T>. This + class defines a single typedef-member type + that is the same type as T but with any top-level array bounds removed; this + is an example of a traits class that performs a transformation on a type: + + +template <typename T> +struct remove_extent +{ typedef T type; }; + +template <typename T, std::size_t N> +struct remove_extent<T[N]> +{ typedef T type; }; + + + The aim of remove_extent + is this: imagine a generic algorithm that is passed an array type as a template + parameter, remove_extent + provides a means of determining the underlying type of the array. For example + remove_extent<int[4][5]>::type would evaluate to the type int[5]. This example also shows that the number of + template parameters in a partial specialization does not have to match the + number in the default template. However, the number of parameters that appear + after the class name do have to match the number and type of the parameters + in the default template. + + + + Optimized copy + + + As an example of how the type traits classes can be used, consider the standard + library algorithm copy: + + +template<typename Iter1, typename Iter2> +Iter2 copy(Iter1 first, Iter1 last, Iter2 out); + + + Obviously, there's no problem writing a generic version of copy that works + for all iterator types Iter1 + and Iter2; however, there are + some circumstances when the copy operation can best be performed by a call + to memcpy. In order to implement + copy in terms of memcpy all + of the following conditions need to be met: + + + + Both of the iterator types Iter1 + and Iter2 must be pointers. + + + Both Iter1 and Iter2 must point to the same type - excluding + const and volatile-qualifiers. + + + The type pointed to by Iter1 + must have a trivial assignment operator. + + + + By trivial assignment operator we mean that the type is either a scalar type[3] or: + + + + The type has no user defined assignment operator. + + + The type does not have any data members that are references. + + + All base classes, and all data member objects must have trivial assignment + operators. + + + + If all these conditions are met then a type can be copied using memcpy rather than using a compiler generated + assignment operator. The type-traits library provides a class has_trivial_assign, + such that has_trivial_assign<T>::value is true only if T has a trivial assignment + operator. This class "just works" for scalar types, but has to be + explicitly specialised for class/struct types that also happen to have a trivial + assignment operator. In other words if has_trivial_assign + gives the wrong answer, it will give the "safe" wrong answer - that + trivial assignment is not allowable. + + + The code for an optimized version of copy that uses memcpy + where appropriate is given in the + examples. The code begins by defining a template function do_copy that performs a "slow but safe" + copy. The last parameter passed to this function may be either a true_type + or a false_type. + Following that there is an overload of docopy that + uses `memcpy`: this time the iterators are required to actually be pointers + to the same type, and the final parameter must be a `_true_type. Finally, the version + of copy calls + docopy`, passing `_has_trivial_assign<value_type>()` + as the final parameter: this will dispatch to the optimized version where appropriate, + otherwise it will call the "slow but safe version". + + + + Was it worth it? + + + It has often been repeated in these columns that "premature optimization + is the root of all evil" [4]. + So the question must be asked: was our optimization premature? To put this + in perspective the timings for our version of copy compared a conventional + generic copy[5] are shown in table + 1. + + + Clearly the optimization makes a difference in this case; but, to be fair, + the timings are loaded to exclude cache miss effects - without this accurate + comparison between algorithms becomes difficult. However, perhaps we can add + a couple of caveats to the premature optimization rule: + + + + If you use the right algorithm for the job in the first place then optimization + will not be required; in some cases, memcpy is the right algorithm. + + + If a component is going to be reused in many places by many people then optimizations + may well be worthwhile where they would not be so for a single case - in + other words, the likelihood that the optimization will be absolutely necessary + somewhere, sometime is that much higher. Just as importantly the perceived + value of the stock implementation will be higher: there is no point standardizing + an algorithm if users reject it on the grounds that there are better, more + heavily optimized versions available. + + + Time taken to copy 1000 elements using `copy<const + T*, T*>` (times in micro-seconds) + + + + + + Version + + + + T + + + + Time + + + + + + + + + "Optimized" copy + + + + char + + + + 0.99 + + + + + + + Conventional copy + + + + char + + + + 8.07 + + + + + + + "Optimized" copy + + + + int + + + + 2.52 + + + + + + + Conventional copy + + + + int + + + + 8.02 + + + + + +
+ + Pair of References + + + The optimized copy example shows how type traits may be used to perform optimization + decisions at compile-time. Another important usage of type traits is to allow + code to compile that otherwise would not do so unless excessive partial specialization + is used. This is possible by delegating partial specialization to the type + traits classes. Our example for this form of usage is a pair that can hold + references [6]. + + + First, let us examine the definition of std::pair, omitting + the comparison operators, default constructor, and template copy constructor + for simplicity: + + +template <typename T1, typename T2> +struct pair +{ +typedef T1 first_type; +typedef T2 second_type; + +T1 first; +T2 second; + +pair(const T1 & nfirst, const T2 & nsecond) +:first(nfirst), second(nsecond) { } +}; + + + Now, this "pair" cannot hold references as it currently stands, because + the constructor would require taking a reference to a reference, which is currently + illegal [7]. Let us consider what + the constructor's parameters would have to be in order to allow "pair" + to hold non-reference types, references, and constant references: + + Required Constructor Argument Types + + + + + + Type of T1 + + + + Type of parameter to initializing constructor + + + + + + + + + T + + + + const T & + + + + + + + T & + + + + T & + + + + + + + const T & + + + + const T & + + + + + +
+ + A little familiarity with the type traits classes allows us to construct a + single mapping that allows us to determine the type of parameter from the type + of the contained class. The type traits classes provide a transformation add_reference, which + adds a reference to its type, unless it is already a reference. + + Using add_reference to synthesize the correct constructor + type + + + + + + Type of T1 + + + + Type of const T1 + + + + Type of add_reference<const T1>::type + + + + + + + + + T + + + + const T + + + + const T & + + + + + + + T & + + + + T & [8] + + + + T & + + + + + + + const T & + + + + const T & + + + + const T & + + + + + +
+ + This allows us to build a primary template definition for pair + that can contain non-reference types, reference types, and constant reference + types: + + +template <typename T1, typename T2> +struct pair +{ +typedef T1 first_type; +typedef T2 second_type; + +T1 first; +T2 second; + +pair(boost::add_reference<const T1>::type nfirst, + boost::add_reference<const T2>::type nsecond) +:first(nfirst), second(nsecond) { } +}; + + + Add back in the standard comparison operators, default constructor, and template + copy constructor (which are all the same), and you have a std::pair that + can hold reference types! + + + This same extension could have been done using partial template specialization + of pair, but to specialize + pair in this way would require + three partial specializations, plus the primary template. Type traits allows + us to define a single primary template that adjusts itself auto-magically to + any of these partial specializations, instead of a brute-force partial specialization + approach. Using type traits in this fashion allows programmers to delegate + partial specialization to the type traits classes, resulting in code that is + easier to maintain and easier to understand. + + + + Conclusion + + + We hope that in this article we have been able to give you some idea of what + type-traits are all about. A more complete listing of the available classes + are in the boost documentation, along with further examples using type traits. + Templates have enabled C++ uses to take the advantage of the code reuse that + generic programming brings; hopefully this article has shown that generic programming + does not have to sink to the lowest common denominator, and that templates + can be optimal as well as generic. + + + + Acknowledgements + + + The authors would like to thank Beman Dawes and Howard Hinnant for their helpful + comments when preparing this article. + + + + References + + + + Nathan C. Myers, C++ Report, June 1995. + + + The type traits library is based upon contributions by Steve Cleary, Beman + Dawes, Howard Hinnant and John Maddock: it can be found at www.boost.org. + + + A scalar type is an arithmetic type (i.e. a built-in integer or floating + point type), an enumeration type, a pointer, a pointer to member, or a const- + or volatile-qualified version of one of these types. + + + This quote is from Donald Knuth, ACM Computing Surveys, December 1974, pg + 268. + + + The test code is available as part of the boost utility library (see algo_opt_examples.cpp), + the code was compiled with gcc 2.95 with all optimisations turned on, tests + were conducted on a 400MHz Pentium II machine running Microsoft Windows 98. + + + John Maddock and Howard Hinnant have submitted a "compressed_pair" + library to Boost, which uses a technique similar to the one described here + to hold references. Their pair also uses type traits to determine if any + of the types are empty, and will derive instead of contain to conserve space + -- hence the name "compressed". + + + This is actually an issue with the C++ Core Language Working Group (issue + #106), submitted by Bjarne Stroustrup. The tentative resolution is to allow + a "reference to a reference to T" to mean the same thing as a "reference + to T", but only in template instantiation, in a method similar to multiple + cv-qualifiers. + + + For those of you who are wondering why this shouldn't be const-qualified, + remember that references are always implicitly constant (for example, you + can't re-assign a reference). Remember also that "const T &" + is something completely different. For this reason, cv-qualifiers on template + type arguments that are references are ignored. + + +
+
+ <link linkend="boost_typetraits.category"> Type Traits by Category</link> +
+ <link linkend="boost_typetraits.category.value_traits"> Type Traits + that Describe the Properties of a Type</link> + + + Foo2 + Bar2 + + These traits are all value traits, which is to say the + traits classes all inherit from integral_constant, + and are used to access some numerical property of a type. Often this is a + simple true or false Boolean value, but in a few cases may be some other + integer value (for example when dealing with type alignments, or array bounds: + see alignment_of, + rank + and extent). + +
+ <link linkend="boost_typetraits.category.value_traits.primary"> Categorizing + a Type</link> + + These traits identify what "kind" of type some type T is. These are split into two groups: + primary traits which are all mutually exclusive, and composite traits that + are compositions of one or more primary traits. + + + For any given type, exactly one primary type trait will inherit from true_type, + and all the others will inherit from false_type, + in other words these traits are mutually exclusive. + + + This means that is_integral<T>::value + and is_floating_point<T>::value + will only ever be true for built-in types; if you want to check for a user-defined + class type that behaves "as if" it is an integral or floating + point type, then use the std::numeric_limits + template instead. + + + Synopsis: + + +template <class T> +struct is_array; + +template <class T> +struct is_class; + +template <class T> +struct is_complex; + +template <class T> +struct is_enum; + +template <class T> +struct is_floating_point; + +template <class T> +struct is_function; + +template <class T> +struct is_integral; + +template <class T> +struct is_member_function_pointer; + +template <class T> +struct is_member_object_pointer; + +template <class T> +struct is_pointer; + +template <class T> +struct is_reference; + +template <class T> +struct is_union; + +template <class T> +struct is_void; + + + The following traits are made up of the union of one or more type categorizations. + A type may belong to more than one of these categories, in addition to + one of the primary categories. + + +template <class T> +struct is_arithmetic; + +template <class T> +struct is_compound; + +template <class T> +struct is_fundamental; + +template <class T> +struct is_member_pointer; + +template <class T> +struct is_object; + +template <class T> +struct is_scalar; + +
+
+ <link linkend="boost_typetraits.category.value_traits.properties"> + General Type Properties</link> + + The following templates describe the general properties of a type. + + + Synopsis: + + +template <class T> +struct alignment_of; + +template <class T> +struct has_nothrow_assign; + +template <class T> +struct has_nothrow_constructor; + +template <class T> +struct has_nothrow_default_constructor; + +template <class T> +struct has_nothrow_copy; + +template <class T> +struct has_nothrow_copy_constructor; + +template <class T> +struct has_trivial_assign; + +template <class T> +struct has_trivial_constructor; + +template <class T> +struct has_trivial_default_constructor; + +template <class T> +struct has_trivial_copy; + +template <class T> +struct has_trivial_copy_constructor; + +template <class T> +struct has_trivial_destructor; + +template <class T> +struct has_virtual_destructor; + +template <class T> +struct is_abstract; + +template <class T> +struct is_const; + +template <class T> +struct is_empty; + +template <class T> +struct is_stateless; + +template <class T> +struct is_pod; + +template <class T> +struct is_polymorphic; + +template <class T> +struct is_signed; + +template <class T> +struct is_unsigned; + +template <class T> +struct is_volatile; + +template <class T, std::size_t N = 0> +struct extent; + +template <class T> +struct rank; + +
+
+ <link linkend="boost_typetraits.category.value_traits.relate"> Relationships + Between Two Types</link> + + These templates determine the whether there is a relationship between two + types: + + + Synopsis: + + +template <class Base, class Derived> +struct is_base_of; + +template <class From, class To> +struct is_convertible; + +template <class T, class U> +struct is_same; + +
+
+
+ <link linkend="boost_typetraits.category.transform"> Type Traits that + Transform One Type to Another</link> + + The following templates transform one type to another, based upon some well-defined + rule. Each template has a single member called type + that is the result of applying the transformation to the template argument + T. + + + Synopsis: + + +template <class T> +struct add_const; + +template <class T> +struct add_cv; + +template <class T> +struct add_pointer; + +template <class T> +struct add_reference; + +template <class T> +struct add_volatile; + +template <class T> +struct decay; + +template <class T> +struct floating_point_promotion; + +template <class T> +struct integral_promotion; + +template <class T> +struct make_signed; + +template <class T> +struct make_unsigned; + +template <class T> +struct promote; + +template <class T> +struct remove_all_extents; + +template <class T> +struct remove_const; + +template <class T> +struct remove_cv; + +template <class T> +struct remove_extent; + +template <class T> +struct remove_pointer; + +template <class T> +struct remove_reference; + +template <class T> +struct remove_volatile; + + + + Broken + Compiler Workarounds: + + + For all of these templates support for partial specialization of class templates + is required to correctly implement the transformation. On the other hand, + practice shows that many of the templates from this category are very useful, + and often essential for implementing some generic libraries. Lack of these + templates is often one of the major limiting factors in porting those libraries + to compilers that do not yet support this language feature. As some of these + compilers are going to be around for a while, and at least one of them is + very wide-spread, it was decided that the library should provide workarounds + where possible. + + + The basic idea behind the workaround is to manually define full specializations + of all type transformation templates for all fundamental types, and all their + 1st and 2nd rank cv-[un]qualified derivative pointer types, and to provide + a user-level macro that will define all the explicit specializations needed + for any user-defined type T. + + + The first part guarantees the successful compilation of something like this: + + +BOOST_STATIC_ASSERT((is_same<char, remove_reference<char&>::type>::value)); +BOOST_STATIC_ASSERT((is_same<char const, remove_reference<char const&>::type>::value)); +BOOST_STATIC_ASSERT((is_same<char volatile, remove_reference<char volatile&>::type>::value)); +BOOST_STATIC_ASSERT((is_same<char const volatile, remove_reference<char const volatile&>::type>::value)); +BOOST_STATIC_ASSERT((is_same<char*, remove_reference<char*&>::type>::value)); +BOOST_STATIC_ASSERT((is_same<char const*, remove_reference<char const*&>::type>::value)); +... +BOOST_STATIC_ASSERT((is_same<char const volatile* const volatile* const volatile, remove_reference<char const volatile* const volatile* const volatile&>::type>::value)); + + + and the second part provides the library's users with a mechanism to make + the above code work not only for char, + int or other built-in type, + but for their own types as well: + + +namespace myspace{ + struct MyClass {}; +} +// declare this at global scope: +BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION(myspace::MyClass) +// transformations on myspace::MyClass now work: +BOOST_STATIC_ASSERT((is_same<myspace::MyClass, remove_reference<myspace::MyClass&>::type>::value)); +BOOST_STATIC_ASSERT((is_same<myspace::MyClass, remove_const<myspace::MyClass const>::type>::value)); +// etc. + + + Note that the macro BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION evaluates + to nothing on those compilers that do support + partial specialization. + +
+
+ <link linkend="boost_typetraits.category.alignment"> Synthesizing Types + with Specific Alignments</link> + + Some low level memory management routines need to synthesize a POD type with + specific alignment properties. The template type_with_alignment + finds the smallest type with a specified alignment, while template aligned_storage + creates a type with a specific size and alignment. + + + Synopsis + + +template <std::size_t Align> +struct type_with_alignment; + +template <std::size_t Size, std::size_t Align> +struct aligned_storage; + +
+
+ <link linkend="boost_typetraits.category.function"> Decomposing Function + Types</link> + + The class template function_traits + extracts information from function types (see also is_function). + This traits class allows you to tell how many arguments a function takes, + what those argument types are, and what the return type is. + + + Synopsis + + +template <std::size_t Align> +struct function_traits; + +
+
+
+ <link linkend="boost_typetraits.user_defined"> User Defined Specializations</link> + + Occationally the end user may need to provide their own specialization for + one of the type traits - typically where intrinsic compiler support is required + to implement a specific trait fully. These specializations should derive from + boost::true_type + or boost::false_type + as appropriate: + + +#include <boost/type_traits/is_pod.hpp> +#include <boost/type_traits/is_class.hpp> +#include <boost/type_traits/is_union.hpp> + +struct my_pod{}; +struct my_union +{ + char c; + int i; +}; + +namespace boost +{ + template<> + struct is_pod<my_pod> : public true_type{}; + + template<> + struct is_pod<my_union> : public true_type{}; + + template<> + struct is_union<my_union> : public true_type{}; + + template<> + struct is_class<my_union> : public false_type{}; +} + +
+
+ <link linkend="boost_typetraits.intrinsics"> Support for Compiler Intrinsics</link> + + There are some traits that can not be implemented within the current C++ language: + to make these traits "just work" with user defined types, some kind + of additional help from the compiler is required. Currently (April 2008) Visual + C++ 8 and 9, GNU GCC 4.3 and MWCW 9 provide the necessary intrinsics, and other + compilers will no doubt follow in due course. + + + The Following traits classes always need compiler support to do the right thing + for all types (but all have safe fallback positions if this support is unavailable): + + + + is_union + + + is_pod + + + has_trivial_constructor + + + has_trivial_copy + + + has_trivial_assign + + + has_trivial_destructor + + + has_nothrow_constructor + + + has_nothrow_copy + + + has_nothrow_assign + + + has_virtual_destructor + + + + The following traits classes can't be portably implemented in the C++ language, + although in practice, the implementations do in fact do the right thing on + all the compilers we know about: + + + + is_empty + + + is_polymorphic + + + + The following traits classes are dependent on one or more of the above: + + + + is_class + + + is_stateless + + + + The hooks for compiler-intrinsic support are defined in boost/type_traits/intrinsics.hpp, + adding support for new compilers is simply a matter of defining one of more + of the following macros: + + Macros for Compiler Intrinsics + + + + + + BOOST_IS_UNION(T) + + + + Should evaluate to true if T is a union type + + + + + + + + + BOOST_IS_POD(T) + + + + Should evaluate to true if T is a POD type + + + + + + + BOOST_IS_EMPTY(T) + + + + Should evaluate to true if T is an empty struct or union + + + + + + + BOOST_HAS_TRIVIAL_CONSTRUCTOR(T) + + + + Should evaluate to true if the default constructor for T is trivial (i.e. + has no effect) + + + + + + + BOOST_HAS_TRIVIAL_COPY(T) + + + + Should evaluate to true if T has a trivial copy constructor (and can + therefore be replaced by a call to memcpy) + + + + + + + BOOST_HAS_TRIVIAL_ASSIGN(T) + + + + Should evaluate to true if T has a trivial assignment operator (and can + therefore be replaced by a call to memcpy) + + + + + + + BOOST_HAS_TRIVIAL_DESTRUCTOR(T) + + + + Should evaluate to true if T has a trivial destructor (i.e. ~T() has + no effect) + + + + + + + BOOST_HAS_NOTHROW_CONSTRUCTOR(T) + + + + Should evaluate to true if T + x; + can not throw + + + + + + + BOOST_HAS_NOTHROW_COPY(T) + + + + Should evaluate to true if T(t) can not throw + + + + + + + BOOST_HAS_NOTHROW_ASSIGN(T) + + + + Should evaluate to true if T + t, + u; + t = + u can not throw + + + + + + + BOOST_HAS_VIRTUAL_DESTRUCTOR(T) + + + + Should evaluate to true T has a virtual destructor + + + + + + + BOOST_IS_ABSTRACT(T) + + + + Should evaluate to true if T is an abstract type + + + + + + + BOOST_IS_BASE_OF(T,U) + + + + Should evaluate to true if T is a base class of U + + + + + + + BOOST_IS_CLASS(T) + + + + Should evaluate to true if T is a class type + + + + + + + BOOST_IS_CONVERTIBLE(T,U) + + + + Should evaluate to true if T is convertible to U + + + + + + + BOOST_IS_ENUM(T) + + + + Should evaluate to true is T is an enum + + + + + + + BOOST_IS_POLYMORPHIC(T) + + + + Should evaluate to true if T is a polymorphic type + + + + + + + BOOST_ALIGNMENT_OF(T) + + + + Should evaluate to the alignment requirements of type T. + + + + + +
+
+
+ <link linkend="boost_typetraits.mpl"> MPL Interoperability</link> + + All the value based traits in this library conform to MPL's requirements for + an Integral + Constant type: that includes a number of rather intrusive workarounds + for broken compilers. + + + Purely as an implementation detail, this means that true_type + inherits from boost::mpl::true_, + false_type + inherits from boost::mpl::false_, + and integral_constant<T, + v> + inherits from boost::mpl::integral_c<T,v> + (provided T is not bool) + +
+
+ <link linkend="boost_typetraits.examples"> Examples</link> +
+ <link linkend="boost_typetraits.examples.copy"> An Optimized Version + of std::copy</link> + + Demonstrates a version of std::copy + that uses has_trivial_assign + to determine whether to use memcpy + to optimise the copy operation (see copy_example.cpp): + + +// +// opt::copy +// same semantics as std::copy +// calls memcpy where appropriate. +// + +namespace detail{ + +template<typename I1, typename I2, bool b> +I2 copy_imp(I1 first, I1 last, I2 out, const boost::integral_constant<bool, b>&) +{ + while(first != last) + { + *out = *first; + ++out; + ++first; + } + return out; +} + +template<typename T> +T* copy_imp(const T* first, const T* last, T* out, const boost::true_type&) +{ + memcpy(out, first, (last-first)*sizeof(T)); + return out+(last-first); +} + + +} + +template<typename I1, typename I2> +inline I2 copy(I1 first, I1 last, I2 out) +{ + // + // We can copy with memcpy if T has a trivial assignment operator, + // and if the iterator arguments are actually pointers (this last + // requirement we detect with overload resolution): + // + typedef typename std::iterator_traits<I1>::value_type value_type; + return detail::copy_imp(first, last, out, boost::has_trivial_assign<value_type>()); +} + +
+
+ <link linkend="boost_typetraits.examples.fill"> An Optimised Version + of std::fill</link> + + Demonstrates a version of std::fill + that uses has_trivial_assign + to determine whether to use memset + to optimise the fill operation (see fill_example.cpp): + + +// +// fill +// same as std::fill, but uses memset where appropriate +// +namespace detail{ + +template <typename I, typename T, bool b> +void do_fill(I first, I last, const T& val, const boost::integral_constant<bool, b>&) +{ + while(first != last) + { + *first = val; + ++first; + } +} + +template <typename T> +void do_fill(T* first, T* last, const T& val, const boost::true_type&) +{ + std::memset(first, val, last-first); +} + +} + +template <class I, class T> +inline void fill(I first, I last, const T& val) +{ + // + // We can do an optimised fill if T has a trivial assignment + // operator and if it's size is one: + // + typedef boost::integral_constant<bool, + ::boost::has_trivial_assign<T>::value && (sizeof(T) == 1)> truth_type; + detail::do_fill(first, last, val, truth_type()); +} + +
+
+ <link linkend="boost_typetraits.examples.destruct"> An Example that + Omits Destructor Calls For Types with Trivial Destructors</link> + + Demonstrates a simple algorithm that uses __has_trivial_destruct + to determine whether to destructors need to be called (see trivial_destructor_example.cpp): + + +// +// algorithm destroy_array: +// The reverse of std::unitialized_copy, takes a block of +// initialized memory and calls destructors on all objects therein. +// + +namespace detail{ + +template <class T> +void do_destroy_array(T* first, T* last, const boost::false_type&) +{ + while(first != last) + { + first->~T(); + ++first; + } +} + +template <class T> +inline void do_destroy_array(T* first, T* last, const boost::true_type&) +{ +} + +} // namespace detail + +template <class T> +inline void destroy_array(T* p1, T* p2) +{ + detail::do_destroy_array(p1, p2, ::boost::has_trivial_destructor<T>()); +} + +
+
+ <link linkend="boost_typetraits.examples.iter"> An improved Version + of std::iter_swap</link> + + Demonstrates a version of std::iter_swap + that use type traits to determine whether an it's arguments are proxying + iterators or not, if they're not then it just does a std::swap + of it's dereferenced arguments (the same as std::iter_swap + does), however if they are proxying iterators then takes special care over + the swap to ensure that the algorithm works correctly for both proxying iterators, + and even iterators of different types (see iter_swap_example.cpp): + + +// +// iter_swap: +// tests whether iterator is a proxying iterator or not, and +// uses optimal form accordingly: +// +namespace detail{ + +template <typename I> +static void do_swap(I one, I two, const boost::false_type&) +{ + typedef typename std::iterator_traits<I>::value_type v_t; + v_t v = *one; + *one = *two; + *two = v; +} +template <typename I> +static void do_swap(I one, I two, const boost::true_type&) +{ + using std::swap; + swap(*one, *two); +} + +} + +template <typename I1, typename I2> +inline void iter_swap(I1 one, I2 two) +{ + // + // See is both arguments are non-proxying iterators, + // and if both iterator the same type: + // + typedef typename std::iterator_traits<I1>::reference r1_t; + typedef typename std::iterator_traits<I2>::reference r2_t; + + typedef boost::integral_constant<bool, + ::boost::is_reference<r1_t>::value + && ::boost::is_reference<r2_t>::value + && ::boost::is_same<r1_t, r2_t>::value> truth_type; + + detail::do_swap(one, two, truth_type()); +} + +
+
+ <link linkend="boost_typetraits.examples.to_double"> Convert Numeric + Types and Enums to double</link> + + Demonstrates a conversion of Numeric + Types and enum types to double: + + +template<class T> +inline double to_double(T const& value) +{ + typedef typename boost::promote<T>::type promoted; + return boost::numeric::converter<double,promoted>::convert(value); +} + +
+
+
+ <link linkend="boost_typetraits.reference"> Alphabetical Reference</link> +
+ <link linkend="boost_typetraits.reference.add_const"> add_const</link> + + one + two + + + template <class T> +struct add_const +{ + typedef see-below type; +}; + + + type: The same type as T + const for all T. + + + C++ Standard Reference: 3.9.3. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/add_const.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + add_const<int>::type + + + + int const + + + + + + + add_const<int&>::type + + + + int& + + + + + + + add_const<int*>::type + + + + int* + const + + + + + + + add_const<int const>::type + + + + int const + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.add_cv"> add_cv</link> + + one + two + three + + + template <class T> +struct add_cv +{ + typedef see-below type; +}; + + + type: The same type as T + const volatile + for all T. + + + C++ Standard Reference: 3.9.3. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/add_cv.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + add_cv<int>::type + + + + int const + volatile + + + + + + + add_cv<int&>::type + + + + int& + + + + + + + add_cv<int*>::type + + + + int* + const volatile + + + + + + + add_cv<int const>::type + + + + int const + volatile + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.add_pointer"> add_pointer</link> + +template <class T> +struct add_pointer +{ + typedef see-below type; +}; + + + type: The same type as remove_reference<T>::type*. + + + The rationale for this template is that it produces the same type as TYPEOF(&t), where + t is an object of type T. + + + C++ Standard Reference: 8.3.1. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/add_pointer.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + add_pointer<int>::type + + + + int* + + + + + + + add_pointer<int const&>::type + + + + int const* + + + + + + + add_pointer<int*>::type + + + + int** + + + + + + + add_pointer<int*&>::type + + + + int** + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.add_reference"> add_reference</link> + +template <class T> +struct add_reference +{ + typedef see-below type; +}; + + + type: If T + is not a reference type then T&, otherwise T. + + + C++ Standard Reference: 8.3.2. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/add_reference.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + add_reference<int>::type + + + + int& + + + + + + + add_reference<int const&>::type + + + + int const& + + + + + + + add_reference<int*>::type + + + + int*& + + + + + + + add_reference<int*&>::type + + + + int*& + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.add_volatile"> add_volatile</link> + + one + + + template <class T> +struct add_volatile +{ + typedef see-below type; +}; + + + type: The same type as T + volatile for all T. + + + C++ Standard Reference: 3.9.3. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/add_volatile.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + add_volatile<int>::type + + + + int volatile + + + + + + + add_volatile<int&>::type + + + + int& + + + + + + + add_volatile<int*>::type + + + + int* + volatile + + + + + + + add_volatile<int const>::type + + + + int const + volatile + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.aligned_storage"> aligned_storage</link> + +template <std::size_t Size, std::size_t Align> +struct aligned_storage +{ + typedef see-below type; +}; + + + type: a built-in or POD type with size + Size and an alignment that + is a multiple of Align. + + + Header: #include + <boost/type_traits/aligned_storage.hpp> + or #include <boost/type_traits.hpp> + +
+
+ <link linkend="boost_typetraits.reference.alignment_of"> alignment_of</link> + +template <class T> +struct alignment_of : public integral_constant<std::size_t, ALIGNOF(T)> {}; + + + Inherits: Class template alignmentof inherits from `_integral_constant<std::size_t, + ALIGNOF(T)>, where + ALIGNOF(T)` is the alignment of type T. + + + Note: strictly speaking you should only rely on the value of ALIGNOF(T) being + a multiple of the true alignment of T, although in practice it does compute + the correct value in all the cases we know about. + + + Header: #include + <boost/type_traits/alignment_of.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + alignment_of<int> + inherits from integral_constant<std::size_t, ALIGNOF(int)>. + + +
+
+ + + alignment_of<char>::type is the type integral_constant<std::size_t, ALIGNOF(char)>. + + +
+
+ + + alignment_of<double>::value is an integral constant expression + with value ALIGNOF(double). + + +
+
+ + + alignment_of<T>::value_type is the type std::size_t. + + +
+
+
+ <link linkend="boost_typetraits.reference.decay"> decay</link> + +template <class T> +struct decay +{ + typedef see-below type; +}; + + + type: Let U + be the result of remove_reference<T>::type, then if U + is an array type, the result is remove_extent<U>*, + otherwise if U is a function + type then the result is U*, otherwise the result is U. + + + C++ Standard Reference: 3.9.1. + + + Header: #include + <boost/type_traits/decay.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + decay<int[2][3]>::type + + + + int[2]* + + + + + + + decay<int(&)[2]>::type + + + + int* + + + + + + + decay<int(&)(double)>::type + + + + int(*)(double) + + + + + + + int(*)(double + + + + int(*)(double) + + + + + + + int(double) + + + + int(*)(double) + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.extent"> extent</link> + +template <class T, std::size_t N = 0> +struct extent : public integral_constant<std::size_t, EXTENT(T,N)> {}; + + + Inherits: Class template extent inherits + from integral_constant<std::size_t, EXTENT(T,N)>, + where EXTENT(T,N) is the number of elements in the N'th array + dimention of type T. + + + If T is not an array type, + or if N > + rank<T>::value, or if the N'th array bound is incomplete, + then EXTENT(T,N) is zero. + + + Header: #include + <boost/type_traits/extent.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + extent<int[1]> inherits from integral_constant<std::size_t, 1>. + + +
+
+ + + extent<double[2][3][4], + 1>::type is the type integral_constant<std::size_t, 3>. + + +
+
+ + + extent<int[4]>::value + is an integral constant expression that evaluates to 4. + + +
+
+ + + extent<int[][2]>::value is an integral constant expression + that evaluates to 0. + + +
+
+ + + extent<int[][2], 1>::value + is an integral constant expression that evaluates to 2. + + +
+
+ + + extent<int*>::value is an integral constant expression + that evaluates to 0. + + +
+
+ + + extent<T>::value_type is the type std::size_t. + + +
+
+
+ <link linkend="boost_typetraits.reference.floating_point_promotion"> + floating_point_promotion</link> +template <class T> +struct floating_point_promotion +{ + typedef see-below type; +}; + + + type: If floating point promotion can be + applied to an rvalue of type T, + then applies floating point promotion to T + and keeps cv-qualifiers of T, + otherwise leaves T unchanged. + + + C++ Standard Reference: 4.6. + + + Header: #include + <boost/type_traits/floating_point_promotion.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + floating_point_promotion<float + const>::type + + + + double const + + + + + + + floating_point_promotion<float&>::type + + + + float& + + + + + + + floating_point_promotion<short>::type + + + + short + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.function_traits"> function_traits</link> + +template <class F> +struct function_traits +{ + static const std::size_t arity = see-below; + typedef see-below result_type; + typedef see-below argN_type; +}; + + + The class template function_traits will only compile if: + + + + The compiler supports partial specialization of class templates. + + + The template argument F + is a function type, note that this is not the same thing as a pointer + to a function. + + + + + function_traits is intended to introspect only C++ functions of the form + R (), R( A1 ), R ( A1, ... etc. ) and not function pointers or class member + functions. To convert a function pointer type to a suitable type use remove_pointer. + + + Function Traits Members + + + + + + Member + + + + Description + + + + + + + + + function_traits<F>::arity + + + + An integral constant expression that gives the number of arguments + accepted by the function type F. + + + + + + + function_traits<F>::result_type + + + + The type returned by function type F. + + + + + + + function_traits<F>::argN_type + + + + The Nth argument type of function type F, + where 1 <= + N <= + arity of F. + + + + + +
Examples + + + + + + Expression + + + + Result + + + + + + + + + function_traits<void (void)>::arity + + + + An integral constant expression that has the value 0. + + + + + + + function_traits<long (int)>::arity + + + + An integral constant expression that has the value 1. + + + + + + + function_traits<long (int, long, double, void*)>::arity + + + + An integral constant expression that has the value 4. + + + + + + + function_traits<void (void)>::result_type + + + + The type void. + + + + + + + function_traits<long (int)>::result_type + + + + The type long. + + + + + + + function_traits<long (int)>::arg1_type + + + + The type int. + + + + + + + function_traits<long (int, long, double, void*)>::arg4_type + + + + The type void*. + + + + + + + function_traits<long (int, long, double, void*)>::arg5_type + + + + A compiler error: there is no arg5_type + since there are only four arguments. + + + + + + + function_traits<long (*)(void)>::arity + + + + A compiler error: argument type is a function pointer, + and not a function type. + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.has_nothrow_assign"> has_nothrow_assign</link> + +template <class T> +struct has_nothrow_assign : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + type with a non-throwing assignment-operator then inherits from true_type, + otherwise inherits from false_type. + Type T must be a complete + type. + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with function types. + + + Without some (as yet unspecified) help from the compiler, has_nothrow_assign + will never report that a class or struct has a non-throwing assignment-operator; + this is always safe, if possibly sub-optimal. Currently (May 2005) only Visual + C++ 8 has the necessary compiler support to ensure that this trait "just + works". + + + Header: #include + <boost/type_traits/has_nothrow_assign.hpp> + or #include <boost/type_traits.hpp> + +
+
+ <link linkend="boost_typetraits.reference.has_nothrow_constructor"> + has_nothrow_constructor</link> +template <class T> +struct has_nothrow_constructor : public true_type-or-false_type {}; + +template <class T> +struct has_nothrow_default_constructor : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + type with a non-throwing default-constructor then inherits from true_type, + otherwise inherits from false_type. + Type T must be a complete + type. + + + These two traits are synonyms for each other. + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with function types. + + + Without some (as yet unspecified) help from the compiler, has_nothrow_constructor + will never report that a class or struct has a non-throwing default-constructor; + this is always safe, if possibly sub-optimal. Currently (May 2005) only Visual + C++ 8 has the necessary compiler intrinsics + to ensure that this trait "just works". + + + Header: #include + <boost/type_traits/has_nothrow_constructor.hpp> + or #include <boost/type_traits.hpp> + +
+
+ <link linkend="boost_typetraits.reference.has_nothrow_copy"> has_nothrow_copy</link> + +template <class T> +struct has_nothrow_copy : public true_type-or-false_type {}; + +template <class T> +struct has_nothrow_copy_constructor : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + type with a non-throwing copy-constructor then inherits from true_type, + otherwise inherits from false_type. + Type T must be a complete + type. + + + These two traits are synonyms for each other. + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with function types. + + + Without some (as yet unspecified) help from the compiler, has_nothrow_copy + will never report that a class or struct has a non-throwing copy-constructor; + this is always safe, if possibly sub-optimal. Currently (May 2005) only Visual + C++ 8 has the necessary compiler intrinsics + to ensure that this trait "just works". + + + Header: #include + <boost/type_traits/has_nothrow_copy.hpp> + or #include <boost/type_traits.hpp> + +
+
+ <link linkend="boost_typetraits.reference.has_nothrow_cp_cons"> has_nothrow_copy_constructor</link> + + See has_nothrow_copy. + +
+
+ <link linkend="boost_typetraits.reference.has_no_throw_def_cons"> has_nothrow_default_constructor</link> + + See has_nothrow_constructor. + +
+
+ <link linkend="boost_typetraits.reference.has_trivial_assign"> has_trivial_assign</link> + +template <class T> +struct has_trivial_assign : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + type with a trivial assignment-operator then inherits from true_type, + otherwise inherits from false_type. + + + If a type has a trivial assignment-operator then the operator has the same + effect as copying the bits of one object to the other: calls to the operator + can be safely replaced with a call to memcpy. + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with function types. + + + Without some (as yet unspecified) help from the compiler, has_trivial_assign + will never report that a user-defined class or struct has a trivial constructor; + this is always safe, if possibly sub-optimal. Currently (May 2005) only MWCW + 9 and Visual C++ 8 have the necessary compiler intrinsics + to detect user-defined classes with trivial constructors. + + + C++ Standard Reference: 12.8p11. + + + Header: #include + <boost/type_traits/has_trivial_assign.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + has_trivial_assign<int> + inherits from true_type. + + +
+
+ + + has_trivial_assign<char*>::type is the type true_type. + + +
+
+ + + has_trivial_assign<int (*)(long)>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + has_trivial_assign<MyClass>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + has_trivial_assign<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.has_trivial_constructor"> + has_trivial_constructor</link> +template <class T> +struct has_trivial_constructor : public true_type-or-false_type {}; + +template <class T> +struct has_trivial_default_constructor : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + type with a trivial default-constructor then inherits from true_type, + otherwise inherits from false_type. + + + These two traits are synonyms for each other. + + + If a type has a trivial default-constructor then the constructor have no + effect: calls to the constructor can be safely omitted. Note that using meta-programming + to omit a call to a single trivial-constructor call is of no benefit whatsoever. + However, if loops and/or exception handling code can also be omitted, then + some benefit in terms of code size and speed can be obtained. + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with function types. + + + Without some (as yet unspecified) help from the compiler, has_trivial_constructor + will never report that a user-defined class or struct has a trivial constructor; + this is always safe, if possibly sub-optimal. Currently (May 2005) only MWCW + 9 and Visual C++ 8 have the necessary compiler intrinsics + to detect user-defined classes with trivial constructors. + + + C++ Standard Reference: 12.1p6. + + + Header: #include + <boost/type_traits/has_trivial_constructor.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + has_trivial_constructor<int> inherits from true_type. + + +
+
+ + + has_trivial_constructor<char*>::type + is the type true_type. + + +
+
+ + + has_trivial_constructor<int (*)(long)>::value + is an integral constant expression that evaluates to true. + + +
+
+ + + has_trivial_constructor<MyClass>::value + is an integral constant expression that evaluates to false. + + +
+
+ + + has_trivial_constructor<T>::value_type + is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.has_trivial_copy"> has_trivial_copy</link> + +template <class T> +struct has_trivial_copy : public true_type-or-false_type {}; + +template <class T> +struct has_trivial_copy_constructor : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + type with a trivial copy-constructor then inherits from true_type, + otherwise inherits from false_type. + + + These two traits are synonyms for each other. + + + If a type has a trivial copy-constructor then the constructor has the same + effect as copying the bits of one object to the other: calls to the constructor + can be safely replaced with a call to memcpy. + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with function types. + + + Without some (as yet unspecified) help from the compiler, has_trivial_copy + will never report that a user-defined class or struct has a trivial constructor; + this is always safe, if possibly sub-optimal. Currently (May 2005) only MWCW + 9 and Visual C++ 8 have the necessary compiler intrinsics + to detect user-defined classes with trivial constructors. + + + C++ Standard Reference: 12.8p6. + + + Header: #include + <boost/type_traits/has_trivial_copy.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + has_trivial_copy<int> + inherits from true_type. + + +
+
+ + + has_trivial_copy<char*>::type is the type true_type. + + +
+
+ + + has_trivial_copy<int (*)(long)>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + has_trivial_copy<MyClass>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + has_trivial_copy<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.has_trivial_cp_cons"> has_trivial_copy_constructor</link> + + See has_trivial_copy. + +
+
+ <link linkend="boost_typetraits.reference.has_trivial_def_cons"> has_trivial_default_constructor</link> + + See has_trivial_constructor. + +
+
+ <link linkend="boost_typetraits.reference.has_trivial_destructor"> has_trivial_destructor</link> + +template <class T> +struct has_trivial_destructor : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + type with a trivial destructor then inherits from true_type, + otherwise inherits from false_type. + + + If a type has a trivial destructor then the destructor has no effect: calls + to the destructor can be safely omitted. Note that using meta-programming + to omit a call to a single trivial-constructor call is of no benefit whatsoever. + However, if loops and/or exception handling code can also be omitted, then + some benefit in terms of code size and speed can be obtained. + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with function types. + + + Without some (as yet unspecified) help from the compiler, has_trivial_destructor + will never report that a user-defined class or struct has a trivial destructor; + this is always safe, if possibly sub-optimal. Currently (May 2005) only MWCW + 9 and Visual C++ 8 have the necessary compiler intrinsics + to detect user-defined classes with trivial constructors. + + + C++ Standard Reference: 12.4p3. + + + Header: #include + <boost/type_traits/has_trivial_destructor.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + has_trivial_destructor<int> inherits from true_type. + + +
+
+ + + has_trivial_destructor<char*>::type + is the type true_type. + + +
+
+ + + has_trivial_destructor<int (*)(long)>::value + is an integral constant expression that evaluates to true. + + +
+
+ + + has_trivial_destructor<MyClass>::value + is an integral constant expression that evaluates to false. + + +
+
+ + + has_trivial_destructor<T>::value_type + is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.has_virtual_destructor"> has_virtual_destructor</link> + +template <class T> +struct has_virtual_destructor : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + type with a virtual destructor then inherits from true_type, + otherwise inherits from false_type. + + + Compiler Compatibility: This trait is provided + for completeness, since it's part of the Technical Report on C++ Library + Extensions. However, there is currently no way to portably implement this + trait. The default version provided always inherits from false_type, + and has to be explicitly specialized for types with virtual destructors unless + the compiler used has compiler intrinsics + that enable the trait to do the right thing: currently (May 2005) only Visual + C++ 8 and GCC-4.3 have the necessary intrinsics. + + + C++ Standard Reference: 12.4. + + + Header: #include + <boost/type_traits/has_virtual_destructor.hpp> + or #include <boost/type_traits.hpp> + +
+
+ <link linkend="boost_typetraits.reference.integral_constant"> integral_constant</link> + +template <class T, T val> +struct integral_constant +{ + typedef integral_constant<T, val> type; + typedef T value_type; + static const T value = val; +}; + +typedef integral_constant<bool, true> true_type; +typedef integral_constant<bool, false> false_type; + + + Class template integral_constant + is the common base class for all the value-based type traits. The two typedef's + true_type and false_type are provided for convenience: + most of the value traits are Boolean properties and so will inherit from + one of these. + +
+
+ <link linkend="boost_typetraits.reference.integral_promotion"> integral_promotion</link> + +template <class T> +struct integral_promotion +{ + typedef see-below type; +}; + + + type: If integral promotion can be applied + to an rvalue of type T, then + applies integral promotion to T + and keeps cv-qualifiers of T, + otherwise leaves T unchanged. + + + C++ Standard Reference: 4.5 except 4.5/3 + (integral bit-field). + + + Header: #include + <boost/type_traits/integral_promotion.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + integral_promotion<short + const>::type + + + + int const + + + + + + + integral_promotion<short&>::type + + + + short& + + + + + + + integral_promotion<enum std::float_round_style>::type + + + + int + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.is_abstract"> is_abstract</link> + +template <class T> +struct is_abstract : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + abstract type then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 10.3. + + + Header: #include + <boost/type_traits/is_abstract.hpp> + or #include <boost/type_traits.hpp> + + + Compiler Compatibility: The compiler must + support DR337 (as of April 2005: GCC 3.4, VC++ 7.1 (and later), Intel C++ + 7 (and later), and Comeau 4.3.2). Otherwise behaves the same as is_polymorphic; + this is the "safe fallback position" for which polymorphic types + are always regarded as potentially abstract. The macro BOOST_NO_IS_ABSTRACT + is used to signify that the implementation is buggy, users should check for + this in their own code if the "safe fallback" is not suitable for + their particular use-case. + + + Examples: + +
+ + + Given: class abc{ virtual ~abc() = 0; }; + + +
+
+ + + is_abstract<abc> + inherits from true_type. + + +
+
+ + + is_abstract<abc>::type is the type true_type. + + +
+
+ + + is_abstract<abc const>::value + is an integral constant expression that evaluates to true. + + +
+
+ + + is_abstract<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_arithmetic"> is_arithmetic</link> + +template <class T> +struct is_arithmetic : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + arithmetic type then inherits from true_type, + otherwise inherits from false_type. + Arithmetic types include integral and floating point types (see also is_integral and + is_floating_point). + + + C++ Standard Reference: 3.9.1p8. + + + Header: #include + <boost/type_traits/is_arithmetic.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_arithmetic<int> + inherits from true_type. + + +
+
+ + + is_arithmetic<char>::type is the type true_type. + + +
+
+ + + is_arithmetic<double>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_arithmetic<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_array"> is_array</link> + +template <class T> +struct is_array : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + array type then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.2 and 8.3.4. + + + Header: #include + <boost/type_traits/is_array.hpp> + or #include <boost/type_traits.hpp> + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can give the wrong result with function types. + + + Examples: + +
+ + + is_array<int[2]> inherits from true_type. + + +
+
+ + + is_array<char[2][3]>::type + is the type true_type. + + +
+
+ + + is_array<double[]>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_array<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_base_of"> is_base_of</link> + +template <class Base, class Derived> +struct is_base_of : public true_type-or-false_type {}; + + + Inherits: If Base is base class of type + Derived or if both types are the same then inherits from true_type, + otherwise inherits from false_type. + + + This template will detect non-public base classes, and ambiguous base classes. + + + Note that is_base_of<X,X> will always inherit from true_type. + This is the case even if X + is not a class type. This is a change in behaviour from Boost-1.33 + in order to track the Technical Report on C++ Library Extensions. + + + Types Base and Derived must not be incomplete types. + + + C++ Standard Reference: 10. + + + Header: #include + <boost/type_traits/is_base_of.hpp> + or #include <boost/type_traits.hpp> + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with function types. There are some older compilers which + will produce compiler errors if Base + is a private base class of Derived, + or if Base is an ambiguous + base of Derived. These compilers + include Borland C++, older versions of Sun Forte C++, Digital Mars C++, and + older versions of EDG based compilers. + + + Examples: + +
+ + + Given: class Base{}; class Derived : + public Base{}; + + +
+
+ + + is_base_of<Base, Derived> + inherits from true_type. + + +
+
+ + + is_base_of<Base, Derived>::type is the type true_type. + + +
+
+ + + is_base_of<Base, Derived>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_base_of<Base, Derived>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_base_of<Base, Base>::value is an integral constant expression + that evaluates to true: a class is regarded as it's + own base. + + +
+
+ + + is_base_of<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_class"> is_class</link> + +template <class T> +struct is_class : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + class type then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.2 and 9.2. + + + Header: #include + <boost/type_traits/is_class.hpp> + or #include <boost/type_traits.hpp> + + + Compiler Compatibility: Without (some as + yet unspecified) help from the compiler, we cannot distinguish between union + and class types, as a result this type will erroneously inherit from true_type for + union types. See also is_union. + Currently (May 2005) only Visual C++ 8 has the necessary compiler intrinsics + to correctly identify union types, and therefore make is_class function correctly. + + + Examples: + +
+ + + Given: class MyClass; then: + + +
+
+ + + is_class<MyClass> + inherits from true_type. + + +
+
+ + + is_class<MyClass const>::type + is the type true_type. + + +
+
+ + + is_class<MyClass>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_class<MyClass&>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_class<MyClass*>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_class<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_complex"> is_complex</link> + +template <class T> +struct is_complex : public true_type-or-false_type {}; + + + Inherits: If T + is a complex number type then true (of type std::complex<U> + for some type U), otherwise + false. + + + C++ Standard Reference: 26.2. + + + Header: #include + <boost/type_traits/is_complex.hpp> + or #include <boost/type_traits.hpp> + +
+
+ <link linkend="boost_typetraits.reference.is_compound"> is_compound</link> + +template <class T> +struct is_compound : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + compound type then inherits from true_type, + otherwise inherits from false_type. + Any type that is not a fundamental type is a compound type (see also is_fundamental). + + + C++ Standard Reference: 3.9.2. + + + Header: #include + <boost/type_traits/is_compound.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_compound<MyClass> + inherits from true_type. + + +
+
+ + + is_compound<MyEnum>::type is the type true_type. + + +
+
+ + + is_compound<int*>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_compound<int&>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_compound<int>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_compound<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_const"> is_const</link> + +template <class T> +struct is_const : public true_type-or-false_type {}; + + + Inherits: If T is a (top level) const-qualified + type then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.3. + + + Header: #include + <boost/type_traits/is_const.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_const<int const> inherits from true_type. + + +
+
+ + + is_const<int const volatile>::type is the type true_type. + + +
+
+ + + is_const<int* const>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_const<int const*>::value + is an integral constant expression that evaluates to false: + the const-qualifier is not at the top level in this case. + + +
+
+ + + is_const<int const&>::value + is an integral constant expression that evaluates to false: + the const-qualifier is not at the top level in this case. + + +
+
+ + + is_const<int>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_const<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_convertible"> is_convertible</link> + +template <class From, class To> +struct is_convertible : public true_type-or-false_type {}; + + + Inherits: If an imaginary lvalue of type + From is convertible to type + To then inherits from true_type, + otherwise inherits from false_type. + + + Type From must not be an incomplete type. + + + Type To must not be an incomplete, or function type. + + + No types are considered to be convertible to array types or abstract-class + types. + + + This template can not detect whether a converting-constructor is public or not: if type To + has a private converting constructor + from type From then instantiating + is_convertible<From, To> + will produce a compiler error. For this reason is_convertible + can not be used to determine whether a type has a public + copy-constructor or not. + + + This template will also produce compiler errors if the conversion is ambiguous, + for example: + + +struct A {}; +struct B : A {}; +struct C : A {}; +struct D : B, C {}; +// This produces a compiler error, the conversion is ambiguous: +bool const y = boost::is_convertible<D*,A*>::value; + + + C++ Standard Reference: 4 and 8.5. + + + Compiler Compatibility: This template is + currently broken with Borland C++ Builder 5 (and earlier), for constructor-based + conversions, and for the Metrowerks 7 (and earlier) compiler in all cases. + If the compiler does not support is_abstract, + then the template parameter To + must not be an abstract type. + + + Header: #include + <boost/type_traits/is_convertible.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_convertible<int, double> + inherits from true_type. + + +
+
+ + + is_convertible<const int, double>::type + is the type true_type. + + +
+
+ + + is_convertible<int* const, int*>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_convertible<int const*, int*>::value + is an integral constant expression that evaluates to false: + the conversion would require a const_cast. + + +
+
+ + + is_convertible<int const&, long>::value + is an integral constant expression that evaluates to true. + + +
+
+ + + is_convertible<int>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_convertible<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_empty"> is_empty</link> + +template <class T> +struct is_empty : public true_type-or-false_type {}; + + + Inherits: If T is an empty class type then + inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 10p5. + + + Header: #include + <boost/type_traits/is_empty.hpp> + or #include <boost/type_traits.hpp> + + + Compiler Compatibility: In order to correctly + detect empty classes this trait relies on either: + + + + the compiler implementing zero sized empty base classes, or + + + the compiler providing intrinsics + to detect empty classes. + + + + Can not be used with incomplete types. + + + Can not be used with union types, until is_union can be made to work. + + + If the compiler does not support partial-specialization of class templates, + then this template can not be used with abstract types. + + + Examples: + +
+ + + Given: struct empty_class + {}; + + +
+
+ + + is_empty<empty_class> + inherits from true_type. + + +
+
+ + + is_empty<empty_class const>::type + is the type true_type. + + +
+
+ + + is_empty<empty_class>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_empty<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_enum"> is_enum</link> + +template <class T> +struct is_enum : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + enum type then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.2 and 7.2. + + + Header: #include + <boost/type_traits/is_enum.hpp> + or #include <boost/type_traits.hpp> + + + Compiler Compatibility: Requires a correctly + functioning is_convertible + template; this means that is_enum is currently broken under Borland C++ Builder + 5, and for the Metrowerks compiler prior to version 8, other compilers should + handle this template just fine. + + + Examples: + +
+ + + Given: enum my_enum + { one, two }; + + +
+
+ + + is_enum<my_enum> + inherits from true_type. + + +
+
+ + + is_enum<my_enum const>::type + is the type true_type. + + +
+
+ + + is_enum<my_enum>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_enum<my_enum&>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_enum<my_enum*>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_enum<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_floating_point"> is_floating_point</link> + +template <class T> +struct is_floating_point : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + floating point type then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.1p8. + + + Header: #include + <boost/type_traits/is_floating_point.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_floating_point<float> + inherits from true_type. + + +
+
+ + + is_floating_point<double>::type is the type true_type. + + +
+
+ + + is_floating_point<long double>::value + is an integral constant expression that evaluates to true. + + +
+
+ + + is_floating_point<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_function"> is_function</link> + +template <class T> +struct is_function : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + function type then inherits from true_type, + otherwise inherits from false_type. + Note that this template does not detect pointers to functions, + or references to functions, these are detected by is_pointer and is_reference respectively: + + +typedef int f1(); // f1 is of function type. +typedef int (f2*)(); // f2 is a pointer to a function. +typedef int (f3&)(); // f3 is a reference to a function. + + + C++ Standard Reference: 3.9.2p1 and 8.3.5. + + + Header: #include + <boost/type_traits/is_function.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_function<int (void)> + inherits from true_type. + + +
+
+ + + is_function<long (double, int)>::type is the type true_type. + + +
+
+ + + is_function<long (double, int)>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_function<long (*)(double, int)>::value is an integral constant expression + that evaluates to false: the argument in this case + is a pointer type, not a function type. + + +
+
+ + + is_function<long (&)(double, int)>::value is an integral constant expression + that evaluates to false: the argument in this case + is a reference to a function, not a function type. + + +
+
+ + + is_function<long (MyClass::*)(double, int)>::value is an integral constant expression + that evaluates to false: the argument in this case + is a pointer to a member function. + + +
+
+ + + is_function<T>::value_type is the type bool. + + +
+ + + Don't confuse function-types with pointers to functions: + + + typedef int + f(double); + + + defines a function type, + + + f foo; + + + declares a prototype for a function of type f, + + + f* + pf = + foo; + + + f& + fr = + foo; + + + declares a pointer and a reference to the function foo. + + + If you want to detect whether some type is a pointer-to-function then use: + + + is_function<remove_pointer<T>::type>::value + && is_pointer<T>::value + + + or for pointers to member functions you can just use is_member_function_pointer + directly. + + +
+
+ <link linkend="boost_typetraits.reference.is_fundamental"> is_fundamental</link> + +template <class T> +struct is_fundamental : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + fundamental type then inherits from true_type, + otherwise inherits from false_type. + Fundamental types include integral, floating point and void types (see also + is_integral, + is_floating_point + and is_void) + + + C++ Standard Reference: 3.9.1. + + + Header: #include + <boost/type_traits/is_fundamental.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_fundamental<int)> + inherits from true_type. + + +
+
+ + + is_fundamental<double const>::type + is the type true_type. + + +
+
+ + + is_fundamental<void>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_fundamental<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_integral"> is_integral</link> + +template <class T> +struct is_integral : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + integral type then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.1p7. + + + Header: #include + <boost/type_traits/is_integral.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_integral<int> + inherits from true_type. + + +
+
+ + + is_integral<const char>::type + is the type true_type. + + +
+
+ + + is_integral<long>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_integral<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_member_function_pointer"> + is_member_function_pointer</link> +template <class T> +struct is_member_function_pointer : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + pointer to a member function then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.2 and 8.3.3. + + + Header: #include + <boost/type_traits/is_member_function_pointer.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_member_function_pointer<int (MyClass::*)(void)> inherits from true_type. + + +
+
+ + + is_member_function_pointer<int (MyClass::*)(char)>::type + is the type true_type. + + +
+
+ + + is_member_function_pointer<int (MyClass::*)(void)const>::value + is an integral constant expression that evaluates to true. + + +
+
+ + + is_member_function_pointer<int (MyClass::*)>::value + is an integral constant expression that evaluates to false: + the argument in this case is a pointer to a data member and not a member + function, see is_member_object_pointer + and is_member_pointer + + +
+
+ + + is_member_function_pointer<T>::value_type + is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_member_object_pointer"> + is_member_object_pointer</link> +template <class T> +struct is_member_object_pointer : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + pointer to a member object (a data member) then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.2 and 8.3.3. + + + Header: #include + <boost/type_traits/is_member_object_pointer.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_member_object_pointer<int (MyClass::*)> inherits from true_type. + + +
+
+ + + is_member_object_pointer<double (MyClass::*)>::type + is the type true_type. + + +
+
+ + + is_member_object_pointer<const int (MyClass::*)>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_member_object_pointer<int (MyClass::*)(void)>::value + is an integral constant expression that evaluates to false: + the argument in this case is a pointer to a member function and not a + member object, see is_member_function_pointer + and is_member_pointer + + +
+
+ + + is_member_object_pointer<T>::value_type + is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_member_pointer"> is_member_pointer</link> + +template <class T> +struct is_member_pointer : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + pointer to a member (either a function or a data member) then inherits from + true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.2 and 8.3.3. + + + Header: #include + <boost/type_traits/is_member_pointer.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_member_pointer<int (MyClass::*)> + inherits from true_type. + + +
+
+ + + is_member_pointer<int (MyClass::*)(char)>::type is the type true_type. + + +
+
+ + + is_member_pointer<int (MyClass::*)(void)const>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_member_pointer<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_object"> is_object</link> + +template <class T> +struct is_object : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + object type then inherits from true_type, + otherwise inherits from false_type. + All types are object types except references, void, and function types. + + + C++ Standard Reference: 3.9p9. + + + Header: #include + <boost/type_traits/is_object.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_object<int> + inherits from true_type. + + +
+
+ + + is_object<int*>::type is the type true_type. + + +
+
+ + + is_object<int (*)(void)>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_object<int (MyClass::*)(void)const>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_object<int &>::value is an integral constant expression + that evaluates to false: reference types are not + objects + + +
+
+ + + is_object<int (double)>::value is an integral constant expression + that evaluates to false: function types are not + objects + + +
+
+ + + is_object<const void>::value + is an integral constant expression that evaluates to false: + void is not an object type + + +
+
+ + + is_object<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_pod"> is_pod</link> + +template <class T> +struct is_pod : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + POD type then inherits from true_type, + otherwise inherits from false_type. + + + POD stands for "Plain old data". Arithmetic types, and enumeration + types, a pointers and pointer to members are all PODs. Classes and unions + can also be POD's if they have no non-static data members that are of reference + or non-POD type, no user defined constructors, no user defined assignment + operators, no private or protected non-static data members, no virtual functions + and no base classes. Finally, a cv-qualified POD is still a POD, as is an + array of PODs. + + + C++ Standard Reference: 3.9p10 and 9p4 (Note + that POD's are also aggregates, see 8.5.1). + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with function types. + + + Without some (as yet unspecified) help from the compiler, ispod + will never report that a class or struct is a POD; this is always safe, if + possibly sub-optimal. Currently (May 2005) only MWCW 9 and Visual C++ 8 have + the necessary compiler-_intrinsics. + + + Header: #include + <boost/type_traits/is_pod.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_pod<int> + inherits from true_type. + + +
+
+ + + is_pod<char*>::type is the type true_type. + + +
+
+ + + is_pod<int (*)(long)>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_pod<MyClass>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_pod<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_pointer"> is_pointer</link> + +template <class T> +struct is_pointer : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + pointer type (includes function pointers, but excludes pointers to members) + then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.2p2 and 8.3.1. + + + Header: #include + <boost/type_traits/is_pointer.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_pointer<int*> + inherits from true_type. + + +
+
+ + + is_pointer<char* const>::type is the type true_type. + + +
+
+ + + is_pointer<int (*)(long)>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_pointer<int (MyClass::*)(long)>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_pointer<int (MyClass::*)>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_pointer<T>::value_type is the type bool. + + +
+ + + is_pointer detects "real" + pointer types only, and not smart pointers. Users + should not specialise is_pointer + for smart pointer types, as doing so may cause Boost (and other third party) + code to fail to function correctly. Users wanting a trait to detect smart + pointers should create their own. However, note that there is no way in + general to auto-magically detect smart pointer types, so such a trait would + have to be partially specialised for each supported smart pointer type. + + +
+
+ <link linkend="boost_typetraits.reference.is_polymorphic"> is_polymorphic</link> + +template <class T> +struct is_polymorphic : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + polymorphic type then inherits from true_type, + otherwise inherits from false_type. + Type T must be a complete + type. + + + C++ Standard Reference: 10.3. + + + Compiler Compatibility: The implementation + requires some knowledge of the compilers ABI, it does actually seem to work + with the majority of compilers though. + + + Header: #include + <boost/type_traits/is_polymorphic.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + Given: class poly{ virtual ~poly(); }; + + +
+
+ + + is_polymorphic<poly> + inherits from true_type. + + +
+
+ + + is_polymorphic<poly const>::type + is the type true_type. + + +
+
+ + + is_polymorphic<poly>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_polymorphic<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_same"> is_same</link> + +template <class T, class U> +struct is_same : public true_type-or-false_type {}; + + + Inherits: If T and U are the same types + then inherits from true_type, + otherwise inherits from false_type. + + + Header: #include + <boost/type_traits/is_same.hpp> + or #include <boost/type_traits.hpp> + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with abstract, incomplete or function types. + + + Examples: + +
+ + + is_same<int, int> + inherits from true_type. + + +
+
+ + + is_same<int, int>::type is the type true_type. + + +
+
+ + + is_same<int, int>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_same<int const, int>::value + is an integral constant expression that evaluates to false. + + +
+
+ + + is_same<int&, int>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_same<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_scalar"> is_scalar</link> + +template <class T> +struct is_scalar : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + scalar type then inherits from true_type, + otherwise inherits from false_type. + Scalar types include integral, floating point, enumeration, pointer, and + pointer-to-member types. + + + C++ Standard Reference: 3.9p10. + + + Header: #include + <boost/type_traits/is_scalar.hpp> + or #include <boost/type_traits.hpp> + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with function types. + + + Examples: + +
+ + + is_scalar<int*> + inherits from true_type. + + +
+
+ + + is_scalar<int>::type is the type true_type. + + +
+
+ + + is_scalar<double>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_scalar<int (*)(long)>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_scalar<int (MyClass::*)(long)>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_scalar<int (MyClass::*)>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_scalar<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_signed"> is_signed</link> + +template <class T> +struct is_signed : public true_type-or-false_type {}; + + + Inherits: If T is an signed integer type + or an enumerated type with an underlying signed integer type, then inherits + from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.1, 7.2. + + + Header: #include + <boost/type_traits/is_signed.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_signed<int> + inherits from true_type. + + +
+
+ + + is_signed<int const volatile>::type is the type true_type. + + +
+
+ + + is_signed<unsigned int>::value + is an integral constant expression that evaluates to false. + + +
+
+ + + is_signed<myclass>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_signed<char>::value is an integral constant expression + whose value depends upon the signedness of type char. + + +
+
+ + + is_signed<long long>::value + is an integral constant expression that evaluates to true. + + +
+
+ + + is_signed<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_stateless"> is_stateless</link> + +template <class T> +struct is_stateless : public true_type-or-false_type {}; + + + Inherits: Ff T is a stateless type then + inherits from true_type, + otherwise from false_type. + + + Type T must be a complete type. + + + A stateless type is a type that has no storage and whose constructors and + destructors are trivial. That means that is_stateless + only inherits from true_type + if the following expression is true: + + +::boost::has_trivial_constructor<T>::value +&& ::boost::has_trivial_copy<T>::value +&& ::boost::has_trivial_destructor<T>::value +&& ::boost::is_class<T>::value +&& ::boost::is_empty<T>::value + + + C++ Standard Reference: 3.9p10. + + + Header: #include + <boost/type_traits/is_stateless.hpp> + or #include <boost/type_traits.hpp> + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + can not be used with function types. + + + Without some (as yet unspecified) help from the compiler, is_stateless will + never report that a class or struct is stateless; this is always safe, if + possibly sub-optimal. Currently (May 2005) only MWCW 9 and Visual C++ 8 have + the necessary compiler intrinsics + to make this template work automatically. + +
+
+ <link linkend="boost_typetraits.reference.is_reference"> is_reference</link> + +template <class T> +struct is_reference : public true_type-or-false_type {}; + + + Inherits: If T is a reference pointer type + then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.2 and 8.3.2. + + + Compiler Compatibility: If the compiler + does not support partial-specialization of class templates, then this template + may report the wrong result for function types, and for types that are both + const and volatile qualified. + + + Header: #include + <boost/type_traits/is_reference.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_reference<int&> + inherits from true_type. + + +
+
+ + + is_reference<int const&>::type + is the type true_type. + + +
+
+ + + is_reference<int (&)(long)>::value is an integral constant expression + that evaluates to true (the argument in this case + is a reference to a function). + + +
+
+ + + is_reference<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_union"> is_union</link> + +template <class T> +struct is_union : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + union type then inherits from true_type, + otherwise inherits from false_type. + Currently requires some kind of compiler support, otherwise unions are identified + as classes. + + + C++ Standard Reference: 3.9.2 and 9.5. + + + Compiler Compatibility: Without (some as + yet unspecified) help from the compiler, we cannot distinguish between union + and class types using only standard C++, as a result this type will never + inherit from true_type, + unless the user explicitly specializes the template for their user-defined + union types, or unless the compiler supplies some unspecified intrinsic that + implements this functionality. Currently (May 2005) only Visual C++ 8 has + the necessary compiler intrinsics + to make this trait "just work" without user intervention. + + + Header: #include + <boost/type_traits/is_union.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_union<void> + inherits from true_type. + + +
+
+ + + is_union<const void>::type + is the type true_type. + + +
+
+ + + is_union<void>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_union<void*>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_union<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_unsigned"> is_unsigned</link> + +template <class T> +struct is_unsigned : public true_type-or-false_type {}; + + + Inherits: If T is an unsigned integer type + or an enumerated type with an underlying unsigned integer type, then inherits + from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.1, 7.2. + + + Header: #include + <boost/type_traits/is_unsigned.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_unsigned<unsigned int> inherits from true_type. + + +
+
+ + + is_unsigned<unsigned int + const volatile>::type + is the type true_type. + + +
+
+ + + is_unsigned<int>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_unsigned<myclass>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_unsigned<char>::value is an integral constant expression + whose value depends upon the signedness of type char. + + +
+
+ + + is_unsigned<unsigned long + long>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_unsigned<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_void"> is_void</link> + +template <class T> +struct is_void : public true_type-or-false_type {}; + + + Inherits: If T is a (possibly cv-qualified) + void type then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.1p9. + + + Header: #include + <boost/type_traits/is_void.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_void<void> + inherits from true_type. + + +
+
+ + + is_void<const void>::type + is the type true_type. + + +
+
+ + + is_void<void>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_void<void*>::value is an integral constant expression + that evaluates to false. + + +
+
+ + + is_void<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.is_volatile"> is_volatile</link> + +template <class T> +struct is_volatile : public true_type-or-false_type {}; + + + Inherits: If T is a (top level) volatile-qualified + type then inherits from true_type, + otherwise inherits from false_type. + + + C++ Standard Reference: 3.9.3. + + + Header: #include + <boost/type_traits/is_volatile.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + is_volatile<volatile int> inherits from true_type. + + +
+
+ + + is_volatile<const volatile + int>::type is the type true_type. + + +
+
+ + + is_volatile<int* volatile>::value is an integral constant expression + that evaluates to true. + + +
+
+ + + is_volatile<int volatile*>::value + is an integral constant expression that evaluates to false: + the volatile qualifier is not at the top level in this case. + + +
+
+ + + is_volatile<T>::value_type is the type bool. + + +
+
+
+ <link linkend="boost_typetraits.reference.make_signed"> make_signed</link> + +template <class T> +struct make_signed +{ + typedef see-below type; +}; + + + type: If T is a signed integer type then + the same type as T, if T is an unsigned integer type then the corresponding + signed type. Otherwise if T is an enumerated or character type (char or wchar_t) + then a signed integer type with the same width as T. + + + If T has any cv-qualifiers then these are also present on the result type. + + + Requires: T must be an integer or enumerated + type, and must not be the type bool. + + + C++ Standard Reference: 3.9.1. + + + Header: #include + <boost/type_traits/make_signed.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + make_signed<int>::type + + + + int + + + + + + + make_signed<unsigned int + const>::type + + + + int const + + + + + + + make_signed<const unsigned + long long>::type + + + + const long + long + + + + + + + make_signed<my_enum>::type + + + + A signed integer type with the same width as the enum. + + + + + + + make_signed<wchar_t>::type + + + + A signed integer type with the same width as wchar_t. + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.make_unsigned"> make_unsigned</link> + +template <class T> +struct make_unsigned +{ + typedef see-below type; +}; + + + type: If T is a unsigned integer type then + the same type as T, if T is an signed integer type then the corresponding + unsigned type. Otherwise if T is an enumerated or character type (char or + wchar_t) then an unsigned integer type with the same width as T. + + + If T has any cv-qualifiers then these are also present on the result type. + + + Requires: T must be an integer or enumerated + type, and must not be the type bool. + + + C++ Standard Reference: 3.9.1. + + + Header: #include + <boost/type_traits/make_unsigned.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + make_signed<int>::type + + + + unsigned int + + + + + + + make_signed<unsigned int + const>::type + + + + unsigned int + const + + + + + + + make_signed<const unsigned + long long>::type + + + + const unsigned + long long + + + + + + + make_signed<my_enum>::type + + + + An unsigned integer type with the same width as the enum. + + + + + + + make_signed<wchar_t>::type + + + + An unsigned integer type with the same width as wchar_t. + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.promote"> promote</link> + +template <class T> +struct promote +{ + typedef see-below type; +}; + + + type: If integral or floating point promotion + can be applied to an rvalue of type T, + then applies integral and floating point promotions to T + and keeps cv-qualifiers of T, + otherwise leaves T unchanged. + See also integral_promotion + and floating_point_promotion. + + + C++ Standard Reference: 4.5 except 4.5/3 + (integral bit-field) and 4.6. + + + Header: #include + <boost/type_traits/promote.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + promote<short volatile>::type + + + + int volatile + + + + + + + promote<float const>::type + + + + double const + + + + + + + promote<short&>::type + + + + short& + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.rank"> rank</link> + +template <class T> +struct rank : public integral_constant<std::size_t, RANK(T)> {}; + + + Inherits: Class template rank inherits from + integral_constant<std::size_t, RANK(T)>, + where RANK(T) is the + number of array dimensions in type T. + + + If T is not an array type, + then RANK(T) is zero. + + + Header: #include + <boost/type_traits/rank.hpp> + or #include <boost/type_traits.hpp> + + + Examples: + +
+ + + rank<int[]> + inherits from integral_constant<std::size_t, 1>. + + +
+
+ + + rank<double[2][3][4]>::type is the type integral_constant<std::size_t, 3>. + + +
+
+ + + rank<int[1]>::value + is an integral constant expression that evaluates to 1. + + +
+
+ + + rank<int[][2]>::value is an integral constant expression + that evaluates to 2. + + +
+
+ + + rank<int*>::value is an integral constant expression + that evaluates to 0. + + +
+
+ + + rank<T>::value_type is the type std::size_t. + + +
+
+
+ <link linkend="boost_typetraits.reference.remove_all_extents"> remove_all_extents</link> + +template <class T> +struct remove_all_extents +{ + typedef see-below type; +}; + + + type: If T + is an array type, then removes all of the array bounds on T, + otherwise leaves T unchanged. + + + C++ Standard Reference: 8.3.4. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/remove_all_extents.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + remove_all_extents<int>::type + + + + int + + + + + + + remove_all_extents<int const[2]>::type + + + + int const + + + + + + + remove_all_extents<int[][2]>::type + + + + int + + + + + + + remove_all_extents<int[2][3][4]>::type + + + + int + + + + + + + remove_all_extents<int const*>::type + + + + int const* + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.remove_const"> remove_const</link> + +template <class T> +struct remove_const +{ + typedef see-below type; +}; + + + type: The same type as T, + but with any top level const-qualifier removed. + + + C++ Standard Reference: 3.9.3. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/remove_const.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + remove_const<int>::type + + + + int + + + + + + + remove_const<int const>::type + + + + int + + + + + + + remove_const<int const + volatile>::type + + + + int volatile + + + + + + + remove_const<int const&>::type + + + + int const& + + + + + + + remove_const<int const*>::type + + + + int const* + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.remove_cv"> remove_cv</link> + +template <class T> +struct remove_cv +{ + typedef see-below type; +}; + + + type: The same type as T, + but with any top level cv-qualifiers removed. + + + C++ Standard Reference: 3.9.3. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/remove_cv.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + remove_cv<int>::type + + + + int + + + + + + + remove_cv<int const>::type + + + + int + + + + + + + remove_cv<int const + volatile>::type + + + + int + + + + + + + remove_cv<int const&>::type + + + + int const& + + + + + + + remove_cv<int const*>::type + + + + int const* + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.remove_extent"> remove_extent</link> + +template <class T> +struct remove_extent +{ + typedef see-below type; +}; + + + type: If T + is an array type, then removes the topmost array bound, otherwise leaves + T unchanged. + + + C++ Standard Reference: 8.3.4. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/remove_extent.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + remove_extent<int>::type + + + + int + + + + + + + remove_extent<int const[2]>::type + + + + int const + + + + + + + remove_extent<int[2][4]>::type + + + + int[4] + + + + + + + remove_extent<int[][2]>::type + + + + int[2] + + + + + + + remove_extent<int const*>::type + + + + int const* + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.remove_pointer"> remove_pointer</link> + +template <class T> +struct remove_pointer +{ + typedef see-below type; +}; + + + type: The same type as T, + but with any pointer modifier removed. + + + C++ Standard Reference: 8.3.1. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/remove_pointer.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + remove_pointer<int>::type + + + + int + + + + + + + remove_pointer<int const*>::type + + + + int const + + + + + + + remove_pointer<int const**>::type + + + + int const* + + + + + + + remove_pointer<int&>::type + + + + int& + + + + + + + remove_pointer<int*&>::type + + + + int*& + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.remove_reference"> remove_reference</link> + +template <class T> +struct remove_reference +{ + typedef see-below type; +}; + + + type: The same type as T, + but with any reference modifier removed. + + + C++ Standard Reference: 8.3.2. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/remove_reference.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + remove_reference<int>::type + + + + int + + + + + + + remove_reference<int const&>::type + + + + int const + + + + + + + remove_reference<int*>::type + + + + int* + + + + + + + remove_reference<int*&>::type + + + + int* + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.remove_volatile"> remove_volatile</link> + +template <class T> +struct remove_volatile +{ + typedef see-below type; +}; + + + type: The same type as T, + but with any top level volatile-qualifier removed. + + + C++ Standard Reference: 3.9.3. + + + Compiler Compatibility: If the compiler + does not support partial specialization of class-templates then this template + will compile, but the member type + will always be the same as type T + except where compiler + workarounds have been applied. + + + Header: #include + <boost/type_traits/remove_volatile.hpp> + or #include <boost/type_traits.hpp> + + Examples + + + + + + Expression + + + + Result Type + + + + + + + + + remove_volatile<int>::type + + + + int + + + + + + + remove_volatile<int volatile>::type + + + + int + + + + + + + remove_volatile<int const + volatile>::type + + + + int const + + + + + + + remove_volatile<int volatile&>::type + + + + int const& + + + + + + + remove_volatile<int volatile*>::type + + + + int const* + + + + + +
+
+
+ <link linkend="boost_typetraits.reference.type_with_alignment"> type_with_alignment</link> + +template <std::size_t Align> +struct type_with_alignment +{ + typedef see-below type; +}; + + + type: a built-in or POD type with an alignment + that is a multiple of Align. + + + Header: #include + <boost/type_traits/type_with_alignment.hpp> + or #include <boost/type_traits.hpp> + +
+
+
+ <link linkend="boost_typetraits.credits"> Credits</link> + + This documentation was pulled together by John Maddock, using Boost.Quickbook + and Boost.DocBook. + + + The original version of this library was created by Steve Cleary, Beman Dawes, + Howard Hinnant, and John Maddock. John Maddock is the current maintainer of + the library. + + + This version of type traits library is based on contributions by Adobe Systems + Inc, David Abrahams, Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant, + Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Thorsten Ottosen, Robert + Ramey and Jeremy Siek. + + + Mat Marcus and Jesse Jones invented, and published + a paper describing, the partial specialization workarounds used in + this library. + + + Aleksey Gurtovoy added MPL integration to the library. + + + The is_convertible + template is based on code originally devised by Andrei Alexandrescu, see "Generic<Programming>: + Mappings between Types and Values". + + + The latest version of this library and documentation can be found at www.boost.org. Bugs, suggestions and discussion + should be directed to boost@lists.boost.org (see www.boost.org/more/mailing_lists.htm#main + for subscription details). + +
+ +
+ This section must not be indexed. + + template <class T> +struct add_const +{ + typedef see-below type; +}; + +
+ +
+ This section contains one block that must not be indexed and one that should be. + + + template <class T> +struct add_const +{ + typedef see-below type; +}; + + + template <class T> +struct add_volatile +{ + typedef see-below type; +}; + +
+ + + + Class Index + + + Typedef Index + + + Macro Index + + + Index Test 1 + + + Index Test 2 + + + + + -- cgit v1.2.3