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[p5sagit/p5-mst-13.2.git] / lib / base.pm

diff --git a/lib/base.pm b/lib/base.pm
index 4c4fb8b..8564c6c 100644 (file)
--- a/lib/base.pm
+++ b/lib/base.pm
@@ -5,7 +5,6 @@ base - Establish IS-A relationship with base class at compile time
 =head1 SYNOPSIS
 
     package Baz;
-
     use base qw(Foo Bar);
 
 =head1 DESCRIPTION
@@ -18,35 +17,78 @@ Roughly similar in effect to
        push @ISA, qw(Foo Bar);
     }
 
+Will also initialize the %FIELDS hash if one of the base classes has
+it.  Multiple inheritance of %FIELDS is not supported.  The 'base'
+pragma will croak if multiple base classes have a %FIELDS hash.  See
+L<fields> for a description of this feature.
+
+When strict 'vars' is in scope, I<base> also lets you assign to @ISA
+without having to declare @ISA with the 'vars' pragma first.
+
+If any of the base classes are not loaded yet, I<base> silently
+C<require>s them (but it won't call the C<import> method).  Whether to
+C<require> a base class package is determined by the absence of a global
+$VERSION in the base package.  If $VERSION is not detected even after
+loading it, I<base> will define $VERSION in the base package, setting it to
+the string C<-1, set by base.pm>.
+
+=head1 HISTORY
+
 This module was introduced with Perl 5.004_04.
 
-=head1 BUGS
+=head1 SEE ALSO
 
-Needs proper documentation!
+L<fields>
 
 =cut
 
 package base;
 
+use 5.006_001;
+our $VERSION = "1.03";
+
 sub import {
     my $class = shift;
+    my $fields_base;
+    my $pkg = caller(0);
 
     foreach my $base (@_) {
-       unless (defined %{"$base\::"}) {
+       next if $pkg->isa($base);
+        my $vglob;
+       if ($vglob = ${"$base\::"}{VERSION} and *$vglob{SCALAR}) {
+          $$vglob = "-1, set by base.pm" unless defined $$vglob;
+        } else {
            eval "require $base";
            # Only ignore "Can't locate" errors from our eval require.
            # Other fatal errors (syntax etc) must be reported.
            die if $@ && $@ !~ /^Can't locate .*? at \(eval /;
-           unless (defined %{"$base\::"}) {
+           unless (%{"$base\::"}) {
                require Carp;
                Carp::croak("Base class package \"$base\" is empty.\n",
                            "\t(Perhaps you need to 'use' the module ",
                            "which defines that package first.)");
            }
+           ${"$base\::VERSION"} = "-1, set by base.pm" unless defined ${"$base\::VERSION"};
        }
+       push @{"$pkg\::ISA"}, $base;
+
+       # A simple test like (defined %{"$base\::FIELDS"}) will
+       # sometimes produce typo warnings because it would create
+       # the hash if it was not present before.
+       my $fglob;
+       if ($fglob = ${"$base\::"}{"FIELDS"} and *$fglob{HASH}) {
+           if ($fields_base) {
+               require Carp;
+               Carp::croak("Can't multiply inherit %FIELDS");
+           } else {
+               $fields_base = $base;
+           }
+       }
+    }
+    if ($fields_base) {
+       require fields;
+       fields::inherit($pkg, $fields_base);
     }
-    
-    push @{caller(0) . '::ISA'}, @_;
 }
 
 1;