93 lines
2.3 KiB
Perl
93 lines
2.3 KiB
Perl
=head1 NAME
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base - Establish IS-A relationship with base class at compile time
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=head1 SYNOPSIS
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package Baz;
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use base qw(Foo Bar);
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=head1 DESCRIPTION
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Roughly similar in effect to
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BEGIN {
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require Foo;
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require Bar;
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push @ISA, qw(Foo Bar);
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}
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Will also initialize the %FIELDS hash if one of the base classes has
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it. Multiple inheritance of %FIELDS is not supported. The 'base'
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pragma will croak if multiple base classes have a %FIELDS hash. See
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L<fields> for a description of this feature.
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When strict 'vars' is in scope I<base> also let you assign to @ISA
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without having to declare @ISA with the 'vars' pragma first.
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If any of the base classes are not loaded yet, I<base> silently
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C<require>s them. Whether to C<require> a base class package is
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determined by the absence of a global $VERSION in the base package.
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If $VERSION is not detected even after loading it, <base> will
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define $VERSION in the base package, setting it to the string
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C<-1, defined by base.pm>.
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=head1 HISTORY
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This module was introduced with Perl 5.004_04.
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=head1 SEE ALSO
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L<fields>
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=cut
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package base;
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use 5.005_64;
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our $VERSION = "1.01";
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sub import {
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my $class = shift;
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my $fields_base;
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my $pkg = caller(0);
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foreach my $base (@_) {
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next if $pkg->isa($base);
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push @{"$pkg\::ISA"}, $base;
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unless (exists ${"$base\::"}{VERSION}) {
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eval "require $base";
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# Only ignore "Can't locate" errors from our eval require.
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# Other fatal errors (syntax etc) must be reported.
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die if $@ && $@ !~ /^Can't locate .*? at \(eval /;
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unless (%{"$base\::"}) {
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require Carp;
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Carp::croak("Base class package \"$base\" is empty.\n",
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"\t(Perhaps you need to 'use' the module ",
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"which defines that package first.)");
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}
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${"$base\::VERSION"} = "-1, set by base.pm"
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unless exists ${"$base\::"}{VERSION};
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}
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# A simple test like (defined %{"$base\::FIELDS"}) will
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# sometimes produce typo warnings because it would create
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# the hash if it was not present before.
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my $fglob;
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if ($fglob = ${"$base\::"}{"FIELDS"} and *$fglob{HASH}) {
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if ($fields_base) {
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require Carp;
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Carp::croak("Can't multiply inherit %FIELDS");
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} else {
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$fields_base = $base;
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}
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}
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}
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if ($fields_base) {
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require fields;
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fields::inherit($pkg, $fields_base);
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}
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}
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1;
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