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diff --git a/upstream/mageia-cauldron/man3pm/attributes.3pm b/upstream/mageia-cauldron/man3pm/attributes.3pm new file mode 100644 index 00000000..ed2fd670 --- /dev/null +++ b/upstream/mageia-cauldron/man3pm/attributes.3pm @@ -0,0 +1,468 @@ +.\" -*- mode: troff; coding: utf-8 -*- +.\" Automatically generated by Pod::Man 5.01 (Pod::Simple 3.43) +.\" +.\" Standard preamble: +.\" ======================================================================== +.de Sp \" Vertical space (when we can't use .PP) +.if t .sp .5v +.if n .sp +.. +.de Vb \" Begin verbatim text +.ft CW +.nf +.ne \\$1 +.. +.de Ve \" End verbatim text +.ft R +.fi +.. +.\" \*(C` and \*(C' are quotes in nroff, nothing in troff, for use with C<>. +.ie n \{\ +. ds C` "" +. ds C' "" +'br\} +.el\{\ +. ds C` +. ds C' +'br\} +.\" +.\" Escape single quotes in literal strings from groff's Unicode transform. +.ie \n(.g .ds Aq \(aq +.el .ds Aq ' +.\" +.\" If the F register is >0, we'll generate index entries on stderr for +.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index +.\" entries marked with X<> in POD. Of course, you'll have to process the +.\" output yourself in some meaningful fashion. +.\" +.\" Avoid warning from groff about undefined register 'F'. +.de IX +.. +.nr rF 0 +.if \n(.g .if rF .nr rF 1 +.if (\n(rF:(\n(.g==0)) \{\ +. if \nF \{\ +. de IX +. tm Index:\\$1\t\\n%\t"\\$2" +.. +. if !\nF==2 \{\ +. nr % 0 +. nr F 2 +. \} +. \} +.\} +.rr rF +.\" ======================================================================== +.\" +.IX Title "attributes 3pm" +.TH attributes 3pm 2023-11-28 "perl v5.38.2" "Perl Programmers Reference Guide" +.\" For nroff, turn off justification. Always turn off hyphenation; it makes +.\" way too many mistakes in technical documents. +.if n .ad l +.nh +.SH NAME +attributes \- get/set subroutine or variable attributes +.SH SYNOPSIS +.IX Header "SYNOPSIS" +.Vb 3 +\& sub foo : method ; +\& my ($x,@y,%z) : Bent = 1; +\& my $s = sub : method { ... }; +\& +\& use attributes (); # optional, to get subroutine declarations +\& my @attrlist = attributes::get(\e&foo); +\& +\& use attributes \*(Aqget\*(Aq; # import the attributes::get subroutine +\& my @attrlist = get \e&foo; +.Ve +.SH DESCRIPTION +.IX Header "DESCRIPTION" +Subroutine declarations and definitions may optionally have attribute lists +associated with them. (Variable \f(CW\*(C`my\*(C'\fR declarations also may, but see the +warning below.) Perl handles these declarations by passing some information +about the call site and the thing being declared along with the attribute +list to this module. In particular, the first example above is equivalent to +the following: +.PP +.Vb 1 +\& use attributes _\|_PACKAGE_\|_, \e&foo, \*(Aqmethod\*(Aq; +.Ve +.PP +The second example in the synopsis does something equivalent to this: +.PP +.Vb 6 +\& use attributes (); +\& my ($x,@y,%z); +\& attributes::\->import(_\|_PACKAGE_\|_, \e$x, \*(AqBent\*(Aq); +\& attributes::\->import(_\|_PACKAGE_\|_, \e@y, \*(AqBent\*(Aq); +\& attributes::\->import(_\|_PACKAGE_\|_, \e%z, \*(AqBent\*(Aq); +\& ($x,@y,%z) = 1; +.Ve +.PP +Yes, that's a lot of expansion. +.PP +\&\fBWARNING\fR: attribute declarations for variables are still evolving. +The semantics and interfaces of such declarations could change in +future versions. They are present for purposes of experimentation +with what the semantics ought to be. Do not rely on the current +implementation of this feature. +.PP +There are only a few attributes currently handled by Perl itself (or +directly by this module, depending on how you look at it.) However, +package-specific attributes are allowed by an extension mechanism. +(See "Package-specific Attribute Handling" below.) +.PP +The setting of subroutine attributes happens at compile time. +Variable attributes in \f(CW\*(C`our\*(C'\fR declarations are also applied at compile time. +However, \f(CW\*(C`my\*(C'\fR variables get their attributes applied at run-time. +This means that you have to \fIreach\fR the run-time component of the \f(CW\*(C`my\*(C'\fR +before those attributes will get applied. For example: +.PP +.Vb 1 +\& my $x : Bent = 42 if 0; +.Ve +.PP +will neither assign 42 to \f(CW$x\fR \fInor\fR will it apply the \f(CW\*(C`Bent\*(C'\fR attribute +to the variable. +.PP +An attempt to set an unrecognized attribute is a fatal error. (The +error is trappable, but it still stops the compilation within that +\&\f(CW\*(C`eval\*(C'\fR.) Setting an attribute with a name that's all lowercase +letters that's not a built-in attribute (such as "foo") will result in +a warning with \fB\-w\fR or \f(CW\*(C`use warnings \*(Aqreserved\*(Aq\*(C'\fR. +.ie n .SS "What ""import"" does" +.el .SS "What \f(CWimport\fP does" +.IX Subsection "What import does" +In the description it is mentioned that +.PP +.Vb 1 +\& sub foo : method; +.Ve +.PP +is equivalent to +.PP +.Vb 1 +\& use attributes _\|_PACKAGE_\|_, \e&foo, \*(Aqmethod\*(Aq; +.Ve +.PP +As you might know this calls the \f(CW\*(C`import\*(C'\fR function of \f(CW\*(C`attributes\*(C'\fR at compile +time with these parameters: 'attributes', the caller's package name, the reference +to the code and 'method'. +.PP +.Vb 1 +\& attributes\->import( _\|_PACKAGE_\|_, \e&foo, \*(Aqmethod\*(Aq ); +.Ve +.PP +So you want to know what \f(CW\*(C`import\*(C'\fR actually does? +.PP +First of all \f(CW\*(C`import\*(C'\fR gets the type of the third parameter ('CODE' in this case). +\&\f(CW\*(C`attributes.pm\*(C'\fR checks if there is a subroutine called \f(CW\*(C`MODIFY_<reftype>_ATTRIBUTES\*(C'\fR +in the caller's namespace (here: 'main'). In this case a +subroutine \f(CW\*(C`MODIFY_CODE_ATTRIBUTES\*(C'\fR is required. Then this +method is called to check if you have used a "bad attribute". +The subroutine call in this example would look like +.PP +.Vb 1 +\& MODIFY_CODE_ATTRIBUTES( \*(Aqmain\*(Aq, \e&foo, \*(Aqmethod\*(Aq ); +.Ve +.PP +\&\f(CW\*(C`MODIFY_<reftype>_ATTRIBUTES\*(C'\fR has to return a list of all "bad attributes". +If there are any bad attributes \f(CW\*(C`import\*(C'\fR croaks. +.PP +(See "Package-specific Attribute Handling" below.) +.SS "Built-in Attributes" +.IX Subsection "Built-in Attributes" +The following are the built-in attributes for subroutines: +.IP lvalue 4 +.IX Item "lvalue" +Indicates that the referenced subroutine is a valid lvalue and can +be assigned to. The subroutine must return a modifiable value such +as a scalar variable, as described in perlsub. +.Sp +This module allows one to set this attribute on a subroutine that is +already defined. For Perl subroutines (XSUBs are fine), it may or may not +do what you want, depending on the code inside the subroutine, with details +subject to change in future Perl versions. You may run into problems with +lvalue context not being propagated properly into the subroutine, or maybe +even assertion failures. For this reason, a warning is emitted if warnings +are enabled. In other words, you should only do this if you really know +what you are doing. You have been warned. +.IP method 4 +.IX Item "method" +Indicates that the referenced subroutine +is a method. A subroutine so marked +will not trigger the "Ambiguous call resolved as CORE::%s" warning. +.IP prototype(..) 4 +.IX Item "prototype(..)" +The "prototype" attribute is an alternate means of specifying a prototype +on a sub. The desired prototype is within the parens. +.Sp +The prototype from the attribute is assigned to the sub immediately after +the prototype from the sub, which means that if both are declared at the +same time, the traditionally defined prototype is ignored. In other words, +\&\f(CW\*(C`sub foo($$) : prototype(@) {}\*(C'\fR is indistinguishable from \f(CW\*(C`sub foo(@){}\*(C'\fR. +.Sp +If illegalproto warnings are enabled, the prototype declared inside this +attribute will be sanity checked at compile time. +.IP const 4 +.IX Item "const" +This experimental attribute, introduced in Perl 5.22, only applies to +anonymous subroutines. It causes the subroutine to be called as soon as +the \f(CW\*(C`sub\*(C'\fR expression is evaluated. The return value is captured and +turned into a constant subroutine. +.PP +The following are the built-in attributes for variables: +.IP shared 4 +.IX Item "shared" +Indicates that the referenced variable can be shared across different threads +when used in conjunction with the threads and threads::shared modules. +.SS "Available Subroutines" +.IX Subsection "Available Subroutines" +The following subroutines are available for general use once this module +has been loaded: +.IP get 4 +.IX Item "get" +This routine expects a single parameter\-\-a reference to a +subroutine or variable. It returns a list of attributes, which may be +empty. If passed invalid arguments, it uses \fBdie()\fR (via Carp::croak) +to raise a fatal exception. If it can find an appropriate package name +for a class method lookup, it will include the results from a +\&\f(CW\*(C`FETCH_\fR\f(CItype\fR\f(CW_ATTRIBUTES\*(C'\fR call in its return list, as described in +"Package-specific Attribute Handling" below. +Otherwise, only built-in attributes will be returned. +.IP reftype 4 +.IX Item "reftype" +This routine expects a single parameter\-\-a reference to a subroutine or +variable. It returns the built-in type of the referenced variable, +ignoring any package into which it might have been blessed. +This can be useful for determining the \fItype\fR value which forms part of +the method names described in "Package-specific Attribute Handling" below. +.PP +Note that these routines are \fInot\fR exported by default. +.SS "Package-specific Attribute Handling" +.IX Subsection "Package-specific Attribute Handling" +\&\fBWARNING\fR: the mechanisms described here are still experimental. Do not +rely on the current implementation. In particular, there is no provision +for applying package attributes to 'cloned' copies of subroutines used as +closures. (See "Making References" in perlref for information on closures.) +Package-specific attribute handling may change incompatibly in a future +release. +.PP +When an attribute list is present in a declaration, a check is made to see +whether an attribute 'modify' handler is present in the appropriate package +(or its \f(CW@ISA\fR inheritance tree). Similarly, when \f(CW\*(C`attributes::get\*(C'\fR is +called on a valid reference, a check is made for an appropriate attribute +\&'fetch' handler. See "EXAMPLES" to see how the "appropriate package" +determination works. +.PP +The handler names are based on the underlying type of the variable being +declared or of the reference passed. Because these attributes are +associated with subroutine or variable declarations, this deliberately +ignores any possibility of being blessed into some package. Thus, a +subroutine declaration uses "CODE" as its \fItype\fR, and even a blessed +hash reference uses "HASH" as its \fItype\fR. +.PP +The class methods invoked for modifying and fetching are these: +.IP FETCH_\fItype\fR_ATTRIBUTES 4 +.IX Item "FETCH_type_ATTRIBUTES" +This method is called with two arguments: the relevant package name, +and a reference to a variable or subroutine for which package-defined +attributes are desired. The expected return value is a list of +associated attributes. This list may be empty. +.IP MODIFY_\fItype\fR_ATTRIBUTES 4 +.IX Item "MODIFY_type_ATTRIBUTES" +This method is called with two fixed arguments, followed by the list of +attributes from the relevant declaration. The two fixed arguments are +the relevant package name and a reference to the declared subroutine or +variable. The expected return value is a list of attributes which were +not recognized by this handler. Note that this allows for a derived class +to delegate a call to its base class, and then only examine the attributes +which the base class didn't already handle for it. +.Sp +The call to this method is currently made \fIduring\fR the processing of the +declaration. In particular, this means that a subroutine reference will +probably be for an undefined subroutine, even if this declaration is +actually part of the definition. +.PP +Calling \f(CWattributes::get()\fR from within the scope of a null package +declaration \f(CW\*(C`package ;\*(C'\fR for an unblessed variable reference will +not provide any starting package name for the 'fetch' method lookup. +Thus, this circumstance will not result in a method call for package-defined +attributes. A named subroutine knows to which symbol table entry it belongs +(or originally belonged), and it will use the corresponding package. +An anonymous subroutine knows the package name into which it was compiled +(unless it was also compiled with a null package declaration), and so it +will use that package name. +.SS "Syntax of Attribute Lists" +.IX Subsection "Syntax of Attribute Lists" +An attribute list is a sequence of attribute specifications, separated by +whitespace or a colon (with optional whitespace). +Each attribute specification is a simple +name, optionally followed by a parenthesised parameter list. +If such a parameter list is present, it is scanned past as for the rules +for the \f(CWq()\fR operator. (See "Quote and Quote-like Operators" in perlop.) +The parameter list is passed as it was found, however, and not as per \f(CWq()\fR. +.PP +Some examples of syntactically valid attribute lists: +.PP +.Vb 4 +\& switch(10,foo(7,3)) : expensive +\& Ugly(\*(Aq\e(") :Bad +\& _5x5 +\& lvalue method +.Ve +.PP +Some examples of syntactically invalid attribute lists (with annotation): +.PP +.Vb 5 +\& switch(10,foo() # ()\-string not balanced +\& Ugly(\*(Aq(\*(Aq) # ()\-string not balanced +\& 5x5 # "5x5" not a valid identifier +\& Y2::north # "Y2::north" not a simple identifier +\& foo + bar # "+" neither a colon nor whitespace +.Ve +.SH EXPORTS +.IX Header "EXPORTS" +.SS "Default exports" +.IX Subsection "Default exports" +None. +.SS "Available exports" +.IX Subsection "Available exports" +The routines \f(CW\*(C`get\*(C'\fR and \f(CW\*(C`reftype\*(C'\fR are exportable. +.SS "Export tags defined" +.IX Subsection "Export tags defined" +The \f(CW\*(C`:ALL\*(C'\fR tag will get all of the above exports. +.SH EXAMPLES +.IX Header "EXAMPLES" +Here are some samples of syntactically valid declarations, with annotation +as to how they resolve internally into \f(CW\*(C`use attributes\*(C'\fR invocations by +perl. These examples are primarily useful to see how the "appropriate +package" is found for the possible method lookups for package-defined +attributes. +.IP 1. 4 +Code: +.Sp +.Vb 3 +\& package Canine; +\& package Dog; +\& my Canine $spot : Watchful ; +.Ve +.Sp +Effect: +.Sp +.Vb 2 +\& use attributes (); +\& attributes::\->import(Canine => \e$spot, "Watchful"); +.Ve +.IP 2. 4 +Code: +.Sp +.Vb 2 +\& package Felis; +\& my $cat : Nervous; +.Ve +.Sp +Effect: +.Sp +.Vb 2 +\& use attributes (); +\& attributes::\->import(Felis => \e$cat, "Nervous"); +.Ve +.IP 3. 4 +Code: +.Sp +.Vb 2 +\& package X; +\& sub foo : lvalue ; +.Ve +.Sp +Effect: +.Sp +.Vb 1 +\& use attributes X => \e&foo, "lvalue"; +.Ve +.IP 4. 4 +Code: +.Sp +.Vb 2 +\& package X; +\& sub Y::x : lvalue { 1 } +.Ve +.Sp +Effect: +.Sp +.Vb 1 +\& use attributes Y => \e&Y::x, "lvalue"; +.Ve +.IP 5. 4 +Code: +.Sp +.Vb 2 +\& package X; +\& sub foo { 1 } +\& +\& package Y; +\& BEGIN { *bar = \e&X::foo; } +\& +\& package Z; +\& sub Y::bar : lvalue ; +.Ve +.Sp +Effect: +.Sp +.Vb 1 +\& use attributes X => \e&X::foo, "lvalue"; +.Ve +.PP +This last example is purely for purposes of completeness. You should not +be trying to mess with the attributes of something in a package that's +not your own. +.SH "MORE EXAMPLES" +.IX Header "MORE EXAMPLES" +.IP 1. 4 +.Vb 2 +\& sub MODIFY_CODE_ATTRIBUTES { +\& my ($class,$code,@attrs) = @_; +\& +\& my $allowed = \*(AqMyAttribute\*(Aq; +\& my @bad = grep { $_ ne $allowed } @attrs; +\& +\& return @bad; +\& } +\& +\& sub foo : MyAttribute { +\& print "foo\en"; +\& } +.Ve +.Sp +This example runs. At compile time +\&\f(CW\*(C`MODIFY_CODE_ATTRIBUTES\*(C'\fR is called. In that +subroutine, we check if any attribute is disallowed and we return a list of +these "bad attributes". +.Sp +As we return an empty list, everything is fine. +.IP 2. 4 +.Vb 2 +\& sub MODIFY_CODE_ATTRIBUTES { +\& my ($class,$code,@attrs) = @_; +\& +\& my $allowed = \*(AqMyAttribute\*(Aq; +\& my @bad = grep{ $_ ne $allowed }@attrs; +\& +\& return @bad; +\& } +\& +\& sub foo : MyAttribute Test { +\& print "foo\en"; +\& } +.Ve +.Sp +This example is aborted at compile time as we use the attribute "Test" which +isn't allowed. \f(CW\*(C`MODIFY_CODE_ATTRIBUTES\*(C'\fR +returns a list that contains a single +element ('Test'). +.SH "SEE ALSO" +.IX Header "SEE ALSO" +"Private Variables via \fBmy()\fR" in perlsub and +"Subroutine Attributes" in perlsub for details on the basic declarations; +"use" in perlfunc for details on the normal invocation mechanism. |