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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:45:59 +0000 |
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| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:45:59 +0000 |
| commit | 19fcec84d8d7d21e796c7624e521b60d28ee21ed (patch) | |
| tree | 42d26aa27d1e3f7c0b8bd3fd14e7d7082f5008dc /src/boost/libs/utility/utility.htm | |
| parent | Initial commit. (diff) | |
| download | ceph-6d07fdb6bb33b1af39833b850bb6cf8af79fe293.tar.xz ceph-6d07fdb6bb33b1af39833b850bb6cf8af79fe293.zip | |
Adding upstream version 16.2.11+ds.upstream/16.2.11+dsupstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/boost/libs/utility/utility.htm')
| -rw-r--r-- | src/boost/libs/utility/utility.htm | 583 |
1 files changed, 583 insertions, 0 deletions
diff --git a/src/boost/libs/utility/utility.htm b/src/boost/libs/utility/utility.htm new file mode 100644 index 000000000..711b58c26 --- /dev/null +++ b/src/boost/libs/utility/utility.htm @@ -0,0 +1,583 @@ +<html> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> + <title>Header boost/utility.hpp Documentation</title> + </head> + <body bgcolor="#FFFFFF" text="#000000"> + <h1><img src="../../boost.png" alt="boost.png (6897 bytes)" align="center" WIDTH="277" HEIGHT="86">Header + <a href="../../boost/utility.hpp">boost/utility.hpp</a></h1> + <p>The entire contents of the header <code><a href="../../boost/utility.hpp"><boost/utility.hpp></a></code> + are in <code>namespace boost</code>.</p> + <h2>Contents</h2> + <ul> + <li> + Class templates supporting the <a href="doc/html/base_from_member.html"> + base-from-member idiom</a></li> + <li> + Function templates <a href="../core/doc/html/core/checked_delete.html">checked_delete() and + checked_array_delete()</a> (moved to the Boost.Core library)</li> + <li> + Function templates <a href="../iterator/doc/html/iterator/algorithms/next_prior.html">next() and prior()</a> (moved to the Boost.Iterator library)</li> + <li> + Class <a href="../core/doc/html/core/noncopyable.html">noncopyable</a> (moved to the Boost.Core library)</li> + <li> + Function template <a href="../core/doc/html/core/addressof.html">addressof()</a> (moved to the Boost.Core library)</li> + <li>Class template <a href="#result_of">result_of</a></li> + <li> + Macro <a href="#BOOST_BINARY">BOOST_BINARY</a></li> + <li><a href="index.html">Other utilities not part of <code>utility.hpp</code></a></li> + </ul> + <h2> + + <h2><a name="result_of">Class template + result_of</a></h2> <p>The class template + <code>result_of</code> helps determine the type of a + call expression. For example, given an lvalue <code>f</code> of + type <code>F</code> and lvalues <code>t1</code>, + <code>t2</code>, ..., <code>t<em>N</em></code> of + types <code>T1</code>, <code>T2</code>, ..., + <code>T<em>N</em></code>, respectively, the type + <code>result_of<F(T1, T2, ..., + T<em>N</em>)>::type</code> defines the result type + of the expression <code>f(t1, t2, + ...,t<em>N</em>)</code>. This implementation permits + the type <code>F</code> to be a function pointer, + function reference, member function pointer, or class + type. By default, <em>N</em> may be any value between 0 and + 16. To change the upper limit, define the macro + <code>BOOST_RESULT_OF_NUM_ARGS</code> to the maximum + value for <em>N</em>. Class template <code>result_of</code> + resides in the header <code><<a + href="../../boost/utility/result_of.hpp">boost/utility/result_of.hpp</a>></code>.</p> + + <p>If your compiler's support for <code>decltype</code> is + adequate, <code>result_of</code> automatically uses it to + deduce the type of the call expression, in which case + <code>result_of<F(T1, T2, ..., + T<em>N</em>)>::type</code> names the type + <code>decltype(boost::declval<F>()(boost::declval<T1>(), + boost::declval<T2>(), ..., + boost::declval<T<em>N</em>>()))</code>, as in the + following example.</p> + + <blockquote> + <pre>struct functor { + template<class T> + T operator()(T x) + { + return x; + } +}; + +typedef boost::result_of< + functor(int) +>::type type; // type is int</pre> + </blockquote> + + <p>You can test whether <code>result_of</code> is using + <code>decltype</code> by checking if the macro + <code>BOOST_RESULT_OF_USE_DECLTYPE</code> is defined after + including <code>result_of.hpp</code>. You can also force + <code>result_of</code> to use <code>decltype</code> by + defining <code>BOOST_RESULT_OF_USE_DECLTYPE</code> prior + to including <code>result_of.hpp</code>.</p> + + <p>If <code>decltype</code> is not used, + then automatic result type deduction of function + objects is not possible. Instead, <code>result_of</code> + uses the following protocol to allow the programmer to + specify a type. When <code>F</code> is a class type with a + member type <code>result_type</code>, + <code>result_of<F(T1, T2, ..., + T<em>N</em>)>::type</code> is + <code>F::result_type</code>. When <code>F</code> does + not contain <code>result_type</code>, + <code>result_of<F(T1, T2, ..., + T<em>N</em>)>::type</code> is <code>F::result<F(T1, + T2, ..., T<em>N</em>)>::type</code> when + <code><em>N</em> > 0</code> or <code>void</code> + when <code><em>N</em> = 0</code>. Note that it is the + responsibility of the programmer to ensure that + function objects accurately advertise their result + type via this protocol, as in the following + example.</p> + + <blockquote> + <pre>struct functor { + template<class> struct result; + + template<class F, class T> + struct result<F(T)> { + typedef T type; + }; + + template<class T> + T operator()(T x) + { + return x; + } +}; + +typedef boost::result_of< + functor(int) +>::type type; // type is int</pre> + </blockquote> + + <p>Since <code>decltype</code> is a new language + feature recently standardized in C++11, + if you are writing a function object + to be used with <code>result_of</code>, for + maximum portability, you might consider following + the above protocol even if your compiler has + proper <code>decltype</code> support. If you wish to continue to + use the protocol on compilers that + support <code>decltype</code>, there are two options: + You can use <code>boost::tr1_result_of</code>, which is also + defined in <code><<a href="../../boost/utility/result_of.hpp">boost/utility/result_of.hpp</a>></code>. + Alternatively, you can define the macro + <code>BOOST_RESULT_OF_USE_TR1</code>, which causes + <code>result_of</code> to use the protocol described + above instead of <code>decltype</code>. If you choose to + follow the protocol, take care to ensure that the + <code>result_type</code> and + <code>result<></code> members accurately + represent the return type of + <code>operator()</code> given a call expression.</p> + + <p>Additionally, <code>boost::result_of</code> + provides a third mode of operation, which some users + may find convenient. When + <code>BOOST_RESULT_OF_USE_TR1_WITH_DECLTYPE_FALLBACK</code> + is defined, <code>boost::result_of</code> behaves as + follows. If the function object has a member + type <code>result_type</code> or member + template <code>result<></code>, then + <code>boost::result_of</code> will use the TR1 + protocol. Otherwise, + <code>boost::result_of</code> will + use <code>decltype</code>. Using TR1 with + a <code>declytpe</code> fallback may workaround + certain problems at the cost of portability. For + example: + <ul> + <li>Deficient compiler: If your code + requires <code>boost::result_of</code> to work + with incomplete return types but your + compiler's <code>decltype</code> implementation + does not support incomplete return types, then you + can use the TR1 protocol as a workaround. Support + for incomplete return types was added late in the + C++11 standardization process + (see <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3276.pdf">N3276</a>) + and is not implemented by some compilers.</li> + + <li>Deficient legacy code: If your existing TR1 + function object advertises a different type than + the actual result type deduced + by <code>decltype</code>, then using TR1 with a + <code>decltype</code> fallback will allow you to + work with both your existing TR1 function objects + and new C++11 function object. This situation + could occur if your legacy function objects + misused the TR1 protocol. See the documentation on + known <a href="#result_of_tr1_diff">differences</a> + between <code>boost::result_of</code> and TR1.</li> + </ul> + + <a name="BOOST_NO_RESULT_OF"></a> + <p>This implementation of <code>result_of</code> + requires class template partial specialization, the + ability to parse function types properly, and support + for SFINAE. If <code>result_of</code> is not supported + by your compiler, including the header + <code>boost/utility/result_of.hpp</code> will + define the macro <code>BOOST_NO_RESULT_OF</code>.</p> + + <p>For additional information + about <code>result_of</code>, see the C++ Library + Technical Report, + <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf">N1836</a>, + or, for motivation and design rationale, + the <code>result_of</code> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1454.html">proposal</a>.</p> + + <a name="result_of_guidelines"> + <h3>Usage guidelines for boost::result_of</h3> + </a> + + <p>The following are general suggestions about when + and how to use <code>boost::result_of</code>.</p> + + <ol> + <li> If you are targeting C++11 and are not concerned + about portability to non-compliant compilers or + previous versions of the standard, then use + <code>std::result_of</code>. If <code>std::result_of</code> + meets your needs, then there's no reason to stop using + it.</li> + + <li> If you are targeting C++11 but may port your code + to legacy compilers at some time in the future, then + use <code>boost::result_of</code> with + <code>decltype</code>. When <code>decltype</code> is + used <code>boost::result_of</code> + and <code>std::result_of</code> are usually + interchangeable. See the documentation on + known <a href="#result_of_cxx11_diff">differences</a> + between boost::result_of and C++11 result_of.</li> + + <li> If compiler portability is required, + use <code>boost::result_of</code> with the TR1 protocol.</li> + </ol> + + <p>Regardless of how you + configure <code>boost::result_of</code>, it is + important to bear in mind that the return type of a + function may change depending on its arguments, and + additionally, the return type of a member function may + change depending on the cv-qualification of the + object. <code>boost::result_of</code> must be passed + the appropriately cv-qualified types in order to + deduce the corresponding return type. For example: + + <blockquote> + <pre>struct functor { + int& operator()(int); + int const& operator()(int) const; + + float& operator()(float&); + float const& operator()(float const&); +}; + +typedef boost::result_of< + functor(int) +>::type type1; // type1 is int & + +typedef boost::result_of< + const functor(int) +>::type type2; // type2 is int const & + +typedef boost::result_of< + functor(float&) +>::type type3; // type3 is float & + +typedef boost::result_of< + functor(float const&) +>::type type4; // type4 is float const &</pre> + </blockquote> + + <a name="result_of_tr1_protocol_guidelines"> + <h3>Usage guidelines for the TR1 result_of protocol</h3> + </a> + + <p>On compliant C++11 + compilers, <code>boost::result_of</code> can + use <code>decltype</code> to deduce the type of any + call expression, including calls to function + objects. However, on pre-C++11 compilers or on + compilers without adequate decltype support, + additional scaffolding is needed from function + objects as described above. The following are + suggestions about how to use the TR1 protocol.</p> + + <ul> + <li>When the return type does not depend on the + argument types or the cv-qualification of the + function object, simply + define <code>result_type</code>. There is no need + to use the <code>result</code> template unless the + return type varies.</li> + + <li>Use the protocol specified type when defining + function prototypes. This can help ensure the + actual return type does not get out of sync with + the protocol specification. For example: + + <blockquote> + <pre>struct functor { + typedef int result_type; + result_type operator()(int); +};</pre> + </blockquote> </li> + + <li>Always specify the <code>result</code> + specialization near the corresponding + <code>operator()</code> overload. This can make it + easier to keep the specializations in sync with the + overloads. For example: + + <blockquote> + <pre>struct functor { + template<class> struct result; + + template<class F> + struct result<F(int)> { + typedef int& type; + }; + result<functor(int)>::type operator()(int); + + template<class F> + struct result<const F(int)> { + typedef int const& type; + }; + result<const functor(int)>::type operator()(int) const; +};</pre> + </blockquote> </li> + + <li>Use type transformations to simplify + the <code>result</code> template specialization. For + example, the following uses + <a href="../type_traits/doc/html/index.html">Boost.TypeTraits</a> + to specialize the <code>result</code> template for + a single <code>operator()</code> that can be called on + both a const and non-const function object with + either an lvalue or rvalue argument. + + <blockquote> + <pre>struct functor { + template<class> struct result; + + template<class F, class T> + struct result<F(T)> + : boost::remove_cv< + typename boost::remove_reference<T>::type + > + {}; + + template<class T> + T operator()(T const& x) const; +};</pre> + </blockquote></li> + </ul> + + <a name="result_of_tr1_diff"> + <h3>Known differences between boost::result_of and TR1 result_of</h3> + </a> + + When using <code>decltype</code>, <code>boost::result_of</code> + ignores the TR1 protocol and instead deduces the + return type of function objects directly + via <code>decltype</code>. In most situations, users + will not notice a difference, so long as they use the + protocol correctly. The following are situations in + which the type deduced + by <code>boost::result_of</code> is known to differ depending on + whether <code>decltype</code> or the TR1 protocol is + used. + + <ul> + <li> TR1 protocol misusage + + <p>When using the TR1 + protocol, <code>boost::result_of</code> cannot + detect whether the actual type of a call to a + function object is the same as the type specified + by the protocol, which allows for the possibility + of inadvertent mismatches between the specified + type and the actual type. When + using <code>decltype</code>, these subtle bugs + may result in compilation errors. For example:</p> + + <blockquote> + <pre>struct functor { + typedef short result_type; + int operator()(short); +}; + +#ifdef BOOST_RESULT_OF_USE_DECLTYPE + +BOOST_STATIC_ASSERT(( + boost::is_same<boost::result_of<functor(short)>::type, int>::value +)); + +#else + +BOOST_STATIC_ASSERT(( + boost::is_same<boost::result_of<functor(short)>::type, short>::value +)); + +#endif</pre> + </blockquote> + + <p>Note that the user can + force <code>boost::result_of</code> to use the TR1 + protocol even on platforms that + support <code>decltype</code> by + defining <code>BOOST_RESULT_OF_USE_TR1</code>.</p></li> + + <li> Nullary function objects + + <p>When using the TR1 protocol, <code>boost::result_of</code> + cannot always deduce the type of calls to + nullary function objects, in which case the + type defaults to void. When using <code>decltype</code>, + <code>boost::result_of</code> always gives the actual type of the + call expression. For example:</p> + + <blockquote> + <pre>struct functor { + template<class> struct result { + typedef int type; + }; + int operator()(); +}; + +#ifdef BOOST_RESULT_OF_USE_DECLTYPE + +BOOST_STATIC_ASSERT(( + boost::is_same<boost::result_of<functor()>::type, int>::value +)); + +#else + +BOOST_STATIC_ASSERT(( + boost::is_same<boost::result_of<functor()>::type, void>::value +)); + +#endif</pre> + </blockquote> + + <p>Note that there are some workarounds for the + nullary function problem. So long as the return + type does not vary, + <code>result_type</code> can always be used to + specify the return type regardless of arity. If the + return type does vary, then the user can + specialize <code>boost::result_of</code> itself for + nullary calls.</p></li> + + <li> Non-class prvalues and cv-qualification + + <p>When using the TR1 + protocol, <code>boost::result_of</code> will + report the cv-qualified type specified + by <code>result_type</code> or + the <code>result</code> template regardless of + the actual cv-qualification of the call + expression. When using + <code>decltype</code>, <code>boost::result_of</code> + will report the actual type of the call expression, + which is not cv-qualified when the expression is a + non-class prvalue. For example:</p> + + <blockquote> + <pre>struct functor { + template<class> struct result; + template<class F, class T> struct result<F(const T)> { + typedef const T type; + }; + + const short operator()(const short); + int const & operator()(int const &); +}; + +// Non-prvalue call expressions work the same with or without decltype. + +BOOST_STATIC_ASSERT(( + boost::is_same< + boost::result_of<functor(int const &)>::type, + int const & +::value +)); + +// Non-class prvalue call expressions are not actually cv-qualified, +// but only the decltype-based result_of reports this accurately. + +#ifdef BOOST_RESULT_OF_USE_DECLTYPE + +BOOST_STATIC_ASSERT(( + boost::is_same< + boost::result_of<functor(const short)>::type, + short +::value +)); + +#else + +BOOST_STATIC_ASSERT(( + boost::is_same< + boost::result_of<functor(const short)>::type, + const short +::value +)); + +#endif</pre> + </blockquote></li> + </ul> + + <a name="result_of_cxx11_diff"> + <h3>Known differences between boost::result_of and C++11 result_of</h3> + </a> + + <p>When using <code>decltype</code>, <code>boost::result_of</code> + implements most of the C++11 result_of + specification. One known exception is that + <code>boost::result_of</code> does not implement the + requirements regarding pointers to member data.</p> + + <p>Created by Doug Gregor. Contributions from Daniel Walker, Eric Niebler, Michel Morin and others</p> + + <h2><a name="BOOST_BINARY">Macro BOOST_BINARY</a></h2> + + <p>The macro <code>BOOST_BINARY</code> is used for the + representation of binary literals. It takes as an argument + a binary number arranged as an arbitrary amount of 1s and 0s in + groupings of length 1 to 8, with groups separated + by spaces. The type of the literal yielded is determined by + the same rules as those of hex and octal + literals (<i>2.13.1p1</i>). By implementation, this macro + expands directly to an octal literal during preprocessing, so + there is no overhead at runtime and the result is useable in + any place that an octal literal would be.</p> + + <p>In order to directly support binary literals with suffixes, + additional macros of the form BOOST_BINARY_XXX are also + provided, where XXX is a standard integer suffix in all capital + letters. In addition, LL and ULL suffixes may be used for representing + long long and unsigned long long types in compilers which provide + them as an extension.</p> + + + <p>The BOOST_BINARY family of macros resides in the header + <a + href="../../boost/utility/binary.hpp"><boost/utility/binary.hpp></a> + which is automatically included by + <a + href="../../boost/utility.hpp"><boost/utility.hpp></a>. + + <p>Contributed by Matt Calabrese.</p><p> + </p><h3>Example</h3> + <blockquote> + <pre> +void foo( int ); + +void foo( unsigned long ); + +void bar() +{ + int value1 = BOOST_BINARY( 100 111000 01 1 110 ); + + unsigned long value2 = BOOST_BINARY_UL( 100 001 ); // unsigned long + + long long value3 = BOOST_BINARY_LL( 11 000 ); // long long if supported + + assert( BOOST_BINARY( 10010 ) + & BOOST_BINARY( 11000 ) + == BOOST_BINARY( 10000 ) + ); + + foo( BOOST_BINARY( 1010 ) ); // calls the first foo + + foo( BOOST_BINARY_LU( 1010 ) ); // calls the second foo +} +</pre></blockquote> + <hr> + <p>Revised <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan +-->04 September, 2008<!--webbot bot="Timestamp" endspan i-checksum="39369" +--> + </p> + <p>© Copyright Beman Dawes 1999-2003.</p> +<p>Distributed under the Boost Software License, Version 1.0. See +<a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a></p> + + </body> +</html> |