X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FUNIVERSAL.pm;h=6c756652fa29f56cd6f927f6f9b3b49d8251aec8;hb=f9a01fbf80a2dfff95a408098b4f01fe2a12e140;hp=6d832c4bea283abd8212c2151971c95d1ce05289;hpb=a66bc3b0c7b47b1405c3f62393e8f35e9a4bbdb8;p=p5sagit%2Fp5-mst-13.2.git diff --git a/lib/UNIVERSAL.pm b/lib/UNIVERSAL.pm index 6d832c4..6c75665 100644 --- a/lib/UNIVERSAL.pm +++ b/lib/UNIVERSAL.pm @@ -1,8 +1,22 @@ package UNIVERSAL; +our $VERSION = '1.04'; + +# UNIVERSAL should not contain any extra subs/methods beyond those +# that it exists to define. The use of Exporter below is a historical +# accident that can't be fixed without breaking code. Note that we +# *don't* set @ISA here, as we don't want all classes/objects inheriting from +# Exporter. It's bad enough that all classes have a import() method +# whenever UNIVERSAL.pm is loaded. require Exporter; -@ISA = qw(Exporter); -@EXPORT_OK = qw(isa can); +@EXPORT_OK = qw(isa can VERSION); + +# Make sure that even though the import method is called, it doesn't do +# anything unless called on UNIVERSAL. +sub import { + return unless $_[0] eq __PACKAGE__; + goto &Exporter::import; +} 1; __END__ @@ -13,76 +27,169 @@ UNIVERSAL - base class for ALL classes (blessed references) =head1 SYNOPSIS - use UNIVERSAL qw(isa); + $is_io = $fd->isa("IO::Handle"); + $is_io = Class->isa("IO::Handle"); + + $does_log = $obj->DOES("Logger"); + $does_log = Class->DOES("Logger"); + + $sub = $obj->can("print"); + $sub = Class->can("print"); - $yes = isa($ref, "HASH"); - $io = $fd->isa("IO::Handle"); - $sub = $obj->can('print'); + $sub = eval { $ref->can("fandango") }; + $ver = $obj->VERSION; + + # but never do this! + $is_io = UNIVERSAL::isa($fd, "IO::Handle"); + $sub = UNIVERSAL::can($obj, "print"); =head1 DESCRIPTION -C is the base class which all bless references will inherit from, -see L +C is the base class from which all blessed references inherit. +See L. + +C provides the following methods: + +=over 4 + +=item C<< $obj->isa( TYPE ) >> + +=item C<< CLASS->isa( TYPE ) >> + +=item C<< eval { VAL->isa( TYPE ) } >> -C provides the following methods +Where =over 4 -=item isa ( TYPE ) +=item C + +is a package name + +=item C<$obj> + +is a blessed reference or a string containing a package name + +=item C + +is a package name + +=item C + +is any of the above or an unblessed reference + +=back + +When used as an instance or class method (C<< $obj->isa( TYPE ) >>), +C returns I if $obj is blessed into package C or +inherits from package C. + +When used as a class method (C<< CLASS->isa( TYPE ) >>, sometimes +referred to as a static method), C returns I if C +inherits from (or is itself) the name of the package C or +inherits from package C. + +If you're not sure what you have (the C case), wrap the method call in an +C block to catch the exception if C is undefined. + +If you want to be sure that you're calling C as a method, not a class, +check the invocant with C from L first: + + use Scalar::Util 'blessed'; + + if ( blessed( $obj ) && $obj->isa("Some::Class") { + ... + } + +=item C<< $obj->DOES( ROLE ) >> + +=item C<< CLASS->DOES( ROLE ) >> + +C checks if the object or class performs the role C. A role is a +named group of specific behavior (often methods of particular names and +signatures), similar to a class, but not necessarily a complete class by +itself. For example, logging or serialization may be roles. + +C and C are similar, in that if either is true, you know that the +object or class on which you call the method can perform specific behavior. +However, C is different from C in that it does not care I the +invocant performs the operations, merely that it does. (C of course +mandates an inheritance relationship. Other relationships include aggregation, +delegation, and mocking.) -C returns I if C is blessed into package C -or inherits from package C. +By default, classes in Perl only perform the C role, as well as the +role of all classes in their inheritance. In other words, by default C +responds identically to C. -C can be called as either a static or object method call. +There is a relationship between roles and classes, as each class implies the +existence of a role of the same name. There is also a relationship between +inheritance and roles, in that a subclass that inherits from an ancestor class +implicitly performs any roles its parent performs. Thus you can use C in +place of C safely, as it will return true in all places where C will +return true (provided that any overridden C I C methods behave +appropriately). -=item can ( METHOD ) +=item C<< $obj->can( METHOD ) >> -C checks if the object has a method called C. If it does -then a reference to the sub is returned. If it does not then I -is returned. +=item C<< CLASS->can( METHOD ) >> -C can be called as either a static or object method call. +=item C<< eval { VAL->can( METHOD ) } >> -=item VERSION ( [ REQUIRE ] ) +C checks if the object or class has a method called C. If it does, +then it returns a reference to the sub. If it does not, then it returns +I. This includes methods inherited or imported by C<$obj>, C, or +C. + +C cannot know whether an object will be able to provide a method through +AUTOLOAD (unless the object's class has overriden C appropriately), so a +return value of I does not necessarily mean the object will not be able +to handle the method call. To get around this some module authors use a forward +declaration (see L) for methods they will handle via AUTOLOAD. For +such 'dummy' subs, C will still return a code reference, which, when +called, will fall through to the AUTOLOAD. If no suitable AUTOLOAD is provided, +calling the coderef will cause an error. + +You may call C as a class (static) method or an object method. + +Again, the same rule about having a valid invocant applies -- use an C +block or C if you need to be extra paranoid. + +=item C C will return the value of the variable C<$VERSION> in the package the object is blessed into. If C is given then it will do a comparison and die if the package version is not greater than or equal to C. -C can be called as either a static or object method call. +C can be called as either a class (static) method or an object +method. =back -C also optionally exports the following subroutines +=head1 EXPORTS -=over 4 +None by default. -=item isa ( VAL, TYPE ) +You may request the import of three functions (C, C, and C), +however it is usually harmful to do so. Please don't do this in new code. -C returns I if the first argument is a reference and either -of the following statements is true. +For example, previous versions of this documentation suggested using C as +a function to determine the type of a reference: -=over 8 + use UNIVERSAL 'isa'; -=item + $yes = isa $h, "HASH"; + $yes = isa "Foo", "Bar"; -C is a blessed reference and is blessed into package C -or inherits from package C +The problem is that this code will I call an overridden C method in +any class. Instead, use C from L for the first case: -=item + use Scalar::Util 'reftype'; -C is a reference to a C of perl variable (er 'HASH') + $yes = reftype( $h ) eq "HASH"; -=back - -=item can ( VAL, METHOD ) +and the method form of C for the second: -If C is a blessed reference which has a method called C, -C returns a reference to the subroutine. If C is not -a blessed reference, or if it does not have a method C, -I is returned. - -=back + $yes = Foo->isa("Bar"); =cut