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Diffstat (limited to 'Master/xemtex/perl/lib/UNIVERSAL.pm')
-rw-r--r-- | Master/xemtex/perl/lib/UNIVERSAL.pm | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/Master/xemtex/perl/lib/UNIVERSAL.pm b/Master/xemtex/perl/lib/UNIVERSAL.pm new file mode 100644 index 00000000000..92b4fcd352a --- /dev/null +++ b/Master/xemtex/perl/lib/UNIVERSAL.pm @@ -0,0 +1,118 @@ +package UNIVERSAL; + +our $VERSION = '1.00'; + +# 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, 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; +*import = \&Exporter::import; +@EXPORT_OK = qw(isa can VERSION); + +1; +__END__ + +=head1 NAME + +UNIVERSAL - base class for ALL classes (blessed references) + +=head1 SYNOPSIS + + $is_io = $fd->isa("IO::Handle"); + $is_io = Class->isa("IO::Handle"); + + $sub = $obj->can("print"); + $sub = Class->can("print"); + + use UNIVERSAL qw( isa can VERSION ); + $yes = isa $ref, "HASH" ; + $sub = can $ref, "fandango" ; + $ver = VERSION $obj ; + +=head1 DESCRIPTION + +C<UNIVERSAL> is the base class which all bless references will inherit from, +see L<perlobj>. + +C<UNIVERSAL> provides the following methods and functions: + +=over 4 + +=item $obj->isa( TYPE ), CLASS->isa( TYPE ), isa( VAL, TYPE ) + + C<TYPE> is a package name + $obj is a blessed reference or a string containing a package name + C<CLASS> is a package name + C<VAL> is any of the above or an unblessed reference + +When used as an instance or class method (C<$obj->isa( TYPE )>), C<isa> +returns I<true> if $obj is blessed into package C<TYPE> or inherits from +package C<TYPE>. + +When used as a class method (C<CLASS->isa( TYPE )>; sometimes referred to as a +static method), C<isa> returns I<true> if C<CLASS> inherits from (or is itself) +the name of the package C<TYPE> or inherits from package C<TYPE>. + +When used as a function, like + + use UNIVERSAL qw( isa ) ; + $yes = isa $h, "HASH"; + $yes = isa "Foo", "Bar"; + +or + + require UNIVERSAL ; + $yes = UNIVERSAL::isa $a, "ARRAY"; + +, C<isa> returns I<true> in the same cases as above and also if C<VAL> is an +unblessed reference to a perl variable of type C<TYPE>, such as "HASH", +"ARRAY", or "Regexp". + +=item $obj->can( METHOD ), CLASS->can( METHOD ), can( VAL, METHOD ) + +C<can> checks if the object or class has a method called C<METHOD>. If it does +then a reference to the sub is returned. If it does not then I<undef> is +returned. This includes methods inherited or imported by C<$obj>, C<CLASS>, or +C<VAL>. + +C<can> cannot know whether an object will be able to provide a method +through AUTOLOAD, so a return value of I<undef> 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<perlsub>) +for methods they will handle via AUTOLOAD. For such 'dummy' subs, C<can> +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. + +C<can> can be called as a class (static) method, an object method, or a +function. + +When used as a function, if C<VAL> is a blessed reference or package name which +has a method called C<METHOD>, C<can> returns a reference to the subroutine. +If C<VAL> is not a blessed reference, or if it does not have a method +C<METHOD>, I<undef> is returned. + +=item VERSION ( [ REQUIRE ] ) + +C<VERSION> will return the value of the variable C<$VERSION> in the +package the object is blessed into. If C<REQUIRE> is given then +it will do a comparison and die if the package version is not +greater than or equal to C<REQUIRE>. + +C<VERSION> can be called as either a class (static) method, an object method or +or a function. + + +=back + +These subroutines should I<not> be imported via S<C<use UNIVERSAL qw(...)>>. +If you want simple local access to them you can do + + *isa = \&UNIVERSAL::isa; + +to import isa into your package. + +=cut |