102 lines
2.3 KiB
Perl
102 lines
2.3 KiB
Perl
package UNIVERSAL;
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# UNIVERSAL should not contain any extra subs/methods beyond those
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# that it exists to define. The use of Exporter below is a historical
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# accident that should be fixed sometime.
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require Exporter;
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*import = \&Exporter::import;
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@EXPORT_OK = qw(isa can);
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1;
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__END__
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=head1 NAME
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UNIVERSAL - base class for ALL classes (blessed references)
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=head1 SYNOPSIS
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$io = $fd->isa("IO::Handle");
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$sub = $obj->can('print');
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$yes = UNIVERSAL::isa($ref, "HASH");
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=head1 DESCRIPTION
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C<UNIVERSAL> is the base class which all bless references will inherit from,
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see L<perlobj>
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C<UNIVERSAL> provides the following methods
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=over 4
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=item isa ( TYPE )
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C<isa> returns I<true> if C<REF> is blessed into package C<TYPE>
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or inherits from package C<TYPE>.
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C<isa> can be called as either a static or object method call.
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=item can ( METHOD )
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C<can> checks if the object has a method called C<METHOD>. If it does
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then a reference to the sub is returned. If it does not then I<undef>
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is returned.
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C<can> can be called as either a static or object method call.
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=item VERSION ( [ REQUIRE ] )
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C<VERSION> will return the value of the variable C<$VERSION> in the
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package the object is blessed into. If C<REQUIRE> is given then
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it will do a comparison and die if the package version is not
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greater than or equal to C<REQUIRE>.
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C<VERSION> can be called as either a static or object method call.
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=back
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The C<isa> and C<can> methods can also be called as subroutines
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=over 4
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=item UNIVERSAL::isa ( VAL, TYPE )
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C<isa> returns I<true> if one of the following statements is true.
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=over 8
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=item *
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C<VAL> is a reference blessed into either package C<TYPE> or a package
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which inherits from package C<TYPE>.
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=item *
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C<VAL> is a reference to a C<TYPE> of Perl variable (e.g. 'HASH').
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=item *
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C<VAL> is the name of a package that inherits from (or is itself)
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package C<TYPE>.
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=back
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=item UNIVERSAL::can ( VAL, METHOD )
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If C<VAL> is a blessed reference which has a method called C<METHOD>,
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C<can> returns a reference to the subroutine. If C<VAL> is not
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a blessed reference, or if it does not have a method C<METHOD>,
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I<undef> is returned.
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=back
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These subroutines should I<not> be imported via S<C<use UNIVERSAL qw(...)>>.
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If you want simple local access to them you can do
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*isa = \&UNIVERSAL::isa;
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to import isa into your package.
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=cut
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