=encoding euc-jp =head1 NAME =begin original attributes - get/set subroutine or variable attributes =end original attributes - サブルーチンや変数の属性を設定/取得する =head1 SYNOPSIS sub foo : method ; my ($x,@y,%z) : Bent = 1; my $s = sub : method { ... }; use attributes (); # optional, to get subroutine declarations my @attrlist = attributes::get(\&foo); use attributes 'get'; # import the attributes::get subroutine my @attrlist = get \&foo; =head1 DESCRIPTION =begin original Subroutine declarations and definitions may optionally have attribute lists associated with them. (Variable C declarations also may, but see the warning below.) Perl handles these declarations by passing some information about the call site and the thing being declared along with the attribute list to this module. In particular, the first example above is equivalent to the following: =end original Subroutine declarations and definitions may optionally have attribute lists associated with them. (Variable C declarations also may, but see the warning below.) Perl handles these declarations by passing some information about the call site and the thing being declared along with the attribute list to this module. In particular, the first example above is equivalent to the following: (TBT) use attributes __PACKAGE__, \&foo, 'method'; =begin original The second example in the synopsis does something equivalent to this: =end original The second example in the synopsis does something equivalent to this: (TBT) use attributes (); my ($x,@y,%z); attributes::->import(__PACKAGE__, \$x, 'Bent'); attributes::->import(__PACKAGE__, \@y, 'Bent'); attributes::->import(__PACKAGE__, \%z, 'Bent'); ($x,@y,%z) = 1; =begin original Yes, that's a lot of expansion. =end original Yes, that's a lot of expansion. (TBT) =begin original B: 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. =end original B: 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. (TBT) =begin original 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 L<"Package-specific Attribute Handling"> below.) =end original 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 L<"Package-specific Attribute Handling"> below.) (TBT) =begin original The setting of subroutine attributes happens at compile time. Variable attributes in C declarations are also applied at compile time. However, C variables get their attributes applied at run-time. This means that you have to I the run-time component of the C before those attributes will get applied. For example: =end original The setting of subroutine attributes happens at compile time. Variable attributes in C declarations are also applied at compile time. However, C variables get their attributes applied at run-time. This means that you have to I the run-time component of the C before those attributes will get applied. For example: (TBT) my $x : Bent = 42 if 0; =begin original will neither assign 42 to $x I will it apply the C attribute to the variable. =end original will neither assign 42 to $x I will it apply the C attribute to the variable. (TBT) =begin original An attempt to set an unrecognized attribute is a fatal error. (The error is trappable, but it still stops the compilation within that C.) 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 B<-w> or C. =end original An attempt to set an unrecognized attribute is a fatal error. (The error is trappable, but it still stops the compilation within that C.) 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 B<-w> or C. (TBT) =head2 What C does =begin original In the description it is mentioned that =end original In the description it is mentioned that (TBT) sub foo : method; =begin original is equivalent to =end original is equivalent to (TBT) use attributes __PACKAGE__, \&foo, 'method'; =begin original As you might know this calls the C function of C at compile time with these parameters: 'attributes', the caller's package name, the reference to the code and 'method'. =end original As you might know this calls the C function of C at compile time with these parameters: 'attributes', the caller's package name, the reference to the code and 'method'. (TBT) attributes->import( __PACKAGE__, \&foo, 'method' ); =begin original So you want to know what C actually does? =end original So you want to know what C actually does? (TBT) =begin original First of all C gets the type of the third parameter ('CODE' in this case). C checks if there is a subroutine called C<< MODIFY__ATTRIBUTES >> in the caller's namespace (here: 'main'). In this case a subroutine C 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 =end original First of all C gets the type of the third parameter ('CODE' in this case). C checks if there is a subroutine called C<< MODIFY__ATTRIBUTES >> in the caller's namespace (here: 'main'). In this case a subroutine C 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 (TBT) MODIFY_CODE_ATTRIBUTES( 'main', \&foo, 'method' ); =begin original C<< MODIFY__ATTRIBUTES >> has to return a list of all "bad attributes". If there are any bad attributes C croaks. =end original C<< MODIFY__ATTRIBUTES >> has to return a list of all "bad attributes". If there are any bad attributes C croaks. (TBT) =begin original (See L<"Package-specific Attribute Handling"> below.) =end original (See L<"Package-specific Attribute Handling"> below.) (TBT) =head2 Built-in Attributes =begin original The following are the built-in attributes for subroutines: =end original The following are the built-in attributes for subroutines: (TBT) =over 4 =item locked =begin original B<5.005 threads only! The use of the "locked" attribute currently only makes sense if you are using the deprecated "Perl 5.005 threads" implementation of threads.> =end original B<5.005 threads only! The use of the "locked" attribute currently only makes sense if you are using the deprecated "Perl 5.005 threads" implementation of threads.> (TBT) =begin original Setting this attribute is only meaningful when the subroutine or method is to be called by multiple threads. When set on a method subroutine (i.e., one marked with the B attribute below), Perl ensures that any invocation of it implicitly locks its first argument before execution. When set on a non-method subroutine, Perl ensures that a lock is taken on the subroutine itself before execution. The semantics of the lock are exactly those of one explicitly taken with the C operator immediately after the subroutine is entered. =end original Setting this attribute is only meaningful when the subroutine or method is to be called by multiple threads. When set on a method subroutine (i.e., one marked with the B attribute below), Perl ensures that any invocation of it implicitly locks its first argument before execution. When set on a non-method subroutine, Perl ensures that a lock is taken on the subroutine itself before execution. The semantics of the lock are exactly those of one explicitly taken with the C operator immediately after the subroutine is entered. (TBT) =item method =begin original Indicates that the referenced subroutine is a method. This has a meaning when taken together with the B attribute, as described there. It also means that a subroutine so marked will not trigger the "Ambiguous call resolved as CORE::%s" warning. =end original Indicates that the referenced subroutine is a method. This has a meaning when taken together with the B attribute, as described there. It also means that a subroutine so marked will not trigger the "Ambiguous call resolved as CORE::%s" warning. (TBT) =item lvalue =begin original 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 L. =end original 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 L. (TBT) =back =begin original For global variables there is C attribute: see L. =end original For global variables there is C attribute: see L. (TBT) =head2 Available Subroutines =begin original The following subroutines are available for general use once this module has been loaded: =end original The following subroutines are available for general use once this module has been loaded: (TBT) =over 4 =item get =begin original 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 die() (via L) 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 C_ATTRIBUTES> call in its return list, as described in L<"Package-specific Attribute Handling"> below. Otherwise, only L will be returned. =end original 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 die() (via L) 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 C_ATTRIBUTES> call in its return list, as described in L<"Package-specific Attribute Handling"> below. Otherwise, only L will be returned. (TBT) =item reftype =begin original 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 I value which forms part of the method names described in L<"Package-specific Attribute Handling"> below. =end original 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 I value which forms part of the method names described in L<"Package-specific Attribute Handling"> below. (TBT) =back =begin original Note that these routines are I exported by default. =end original Note that these routines are I exported by default. (TBT) =head2 Package-specific Attribute Handling =begin original B: 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 L for information on closures.) Package-specific attribute handling may change incompatibly in a future release. =end original B: 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 L for information on closures.) Package-specific attribute handling may change incompatibly in a future release. (TBT) =begin original 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 @ISA inheritance tree). Similarly, when C is called on a valid reference, a check is made for an appropriate attribute 'fetch' handler. See L<"EXAMPLES"> to see how the "appropriate package" determination works. =end original 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 @ISA inheritance tree). Similarly, when C is called on a valid reference, a check is made for an appropriate attribute 'fetch' handler. See L<"EXAMPLES"> to see how the "appropriate package" determination works. (TBT) =begin original 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 I, and even a blessed hash reference uses "HASH" as its I. =end original 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 I, and even a blessed hash reference uses "HASH" as its I. (TBT) =begin original The class methods invoked for modifying and fetching are these: =end original The class methods invoked for modifying and fetching are these: (TBT) =over 4 =item FETCH_I_ATTRIBUTES =begin original 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. =end original 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. (TBT) =item MODIFY_I_ATTRIBUTES =begin original 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. =end original 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. (TBT) =begin original The call to this method is currently made I 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. =end original The call to this method is currently made I 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. (TBT) =back =begin original Calling C from within the scope of a null package declaration C 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. =end original Calling C from within the scope of a null package declaration C 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. (TBT) =head2 Syntax of Attribute Lists =begin original 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 C operator. (See L.) The parameter list is passed as it was found, however, and not as per C. =end original 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 C operator. (See L.) The parameter list is passed as it was found, however, and not as per C. (TBT) =begin original Some examples of syntactically valid attribute lists: =end original Some examples of syntactically valid attribute lists: (TBT) switch(10,foo(7,3)) : expensive Ugly('\(") :Bad _5x5 locked method =begin original Some examples of syntactically invalid attribute lists (with annotation): =end original Some examples of syntactically invalid attribute lists (with annotation): (TBT) switch(10,foo() # ()-string not balanced Ugly('(') # ()-string not balanced 5x5 # "5x5" not a valid identifier Y2::north # "Y2::north" not a simple identifier foo + bar # "+" neither a colon nor whitespace =head1 EXPORTS =head2 Default exports =begin original None. =end original None. (TBT) =head2 Available exports =begin original The routines C and C are exportable. =end original The routines C and C are exportable. (TBT) =head2 Export tags defined =begin original The C<:ALL> tag will get all of the above exports. =end original The C<:ALL> tag will get all of the above exports. (TBT) =head1 EXAMPLES =begin original Here are some samples of syntactically valid declarations, with annotation as to how they resolve internally into C 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. =end original Here are some samples of syntactically valid declarations, with annotation as to how they resolve internally into C 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. (TBT) =over 4 =item 1. =begin original Code: =end original Code: (TBT) package Canine; package Dog; my Canine $spot : Watchful ; =begin original Effect: =end original Effect: (TBT) use attributes (); attributes::->import(Canine => \$spot, "Watchful"); =item 2. =begin original Code: =end original Code: (TBT) package Felis; my $cat : Nervous; =begin original Effect: =end original Effect: (TBT) use attributes (); attributes::->import(Felis => \$cat, "Nervous"); =item 3. =begin original Code: =end original Code: (TBT) package X; sub foo : locked ; =begin original Effect: =end original Effect: (TBT) use attributes X => \&foo, "locked"; =item 4. =begin original Code: =end original Code: (TBT) package X; sub Y::x : locked { 1 } =begin original Effect: =end original Effect: (TBT) use attributes Y => \&Y::x, "locked"; =item 5. =begin original Code: =end original Code: (TBT) package X; sub foo { 1 } package Y; BEGIN { *bar = \&X::foo; } package Z; sub Y::bar : locked ; =begin original Effect: =end original Effect: (TBT) use attributes X => \&X::foo, "locked"; =back =begin original This last example is purely for purposes of completeness. You should not be trying to mess with the attributes of something in a package that's not your own. =end original This last example is purely for purposes of completeness. You should not be trying to mess with the attributes of something in a package that's not your own. (TBT) =head1 MORE EXAMPLES =over 4 =item 1. sub MODIFY_CODE_ATTRIBUTES { my ($class,$code,@attrs) = @_; my $allowed = 'MyAttribute'; my @bad = grep { $_ ne $allowed } @attrs; return @bad; } sub foo : MyAttribute { print "foo\n"; } =begin original This example runs. At compile time C is called. In that subroutine, we check if any attribute is disallowed and we return a list of these "bad attributes". =end original This example runs. At compile time C is called. In that subroutine, we check if any attribute is disallowed and we return a list of these "bad attributes". (TBT) =begin original As we return an empty list, everything is fine. =end original As we return an empty list, everything is fine. (TBT) =item 2. sub MODIFY_CODE_ATTRIBUTES { my ($class,$code,@attrs) = @_; my $allowed = 'MyAttribute'; my @bad = grep{ $_ ne $allowed }@attrs; return @bad; } sub foo : MyAttribute Test { print "foo\n"; } =begin original This example is aborted at compile time as we use the attribute "Test" which isn't allowed. C returns a list that contains a single element ('Test'). =end original This example is aborted at compile time as we use the attribute "Test" which isn't allowed. C returns a list that contains a single element ('Test'). (TBT) =back =head1 SEE ALSO =begin original L and L for details on the basic declarations; L for the obsolescent form of subroutine attribute specification which this module replaces; L for details on the normal invocation mechanism. =end original L and L for details on the basic declarations; L for the obsolescent form of subroutine attribute specification which this module replaces; L for details on the normal invocation mechanism. (TBT) =cut