From f1192ceea6b2a126a4ff3254f91c2bc47c361c71 Mon Sep 17 00:00:00 2001
From: Gisle Aas <gisle@aas.no>
Date: Mon, 29 Jun 1998 14:36:09 +0200
Subject: Re: [PATCH] Simplified magic_setisa() and improved fields.pm

	Message-Id: <m367hk4hra.fsf@furu.g.aas.no>

p4raw-id: //depot/perl@1266
---
 lib/base.pm | 35 ++++++++++++++++++++++++++++++-----
 1 file changed, 30 insertions(+), 5 deletions(-)

(limited to 'lib/base.pm')

diff --git a/lib/base.pm b/lib/base.pm
index 4c4fb8b86b..3500cbfb89 100644
--- 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
@@ -18,11 +17,19 @@ 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 has a %FIELDS hash.  See
+L<fields> for a description of this feature.
+
+When strict 'vars' is in scope I<base> also let you assign to @ISA
+without having to declare @ISA with the 'vars' pragma first.
+
 This module was introduced with Perl 5.004_04.
 
-=head1 BUGS
+=head1 SEE ALSO
 
-Needs proper documentation!
+L<fields>
 
 =cut
 
@@ -30,6 +37,7 @@ package base;
 
 sub import {
     my $class = shift;
+    my $fields_base;
 
     foreach my $base (@_) {
 	unless (defined %{"$base\::"}) {
@@ -44,9 +52,26 @@ sub import {
 			    "which defines that package first.)");
 	    }
 	}
+
+	# 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;
+	    }
+	}
+    }
+    my $pkg = caller(0);
+    push @{"$pkg\::ISA"}, @_;
+    if ($fields_base) {
+	require fields;
+	fields::inherit($pkg, $fields_base);
     }
-    
-    push @{caller(0) . '::ISA'}, @_;
 }
 
 1;
-- 
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