Re: goto superclass method

Unfortunately, this doesn't work in vanilla Perl:

#!/usr/bin/perl
use strict;
use warnings;

sub Foo::method { return "Foo" }

BEGIN { @Bar::ISA = qw( Foo ); }

sub Bar::method { goto $_[ 0 ]->SUPER::can( 'method' ); }

print Bar->method(), "\n";
[download]

This is an infinite loop, because it dispatches to UNIVERSAL::can with $_[ 0 ] as the first parameter. This means that adorning the call with SUPER:: doesn't make a difference here. And since the package for $_[ 0 ] is Bar, can() finds Bar::method, so round and round we go…

But we can easily make this work. I came up with this before reading steves' reply, but it is just a cleaner, more polished version of that trick. Stick this somewhere in the code:

sub SUPER::can { my $caller = ( caller 1 )[ 3 ]; no strict 'refs'; local *$caller; return UNIVERSAL::can( @_ ); }
[download]

Tiny as it is, maybe this ought to be on CPAN?

See replies.

Makeshifts last the longest.

Comment on Re: goto superclass method Select or Download Code

Replies are listed 'Best First'.
•Re^2: goto superclass method by merlyn (Sage) on Dec 22, 2004 at 21:34 UTC
This is an infinite loop It's an infinite loop, but not for the reasons you state. SUPER:: is always relative to __PACKAGE__, and when you start saying sub Foo::bar, the __PACKAGE__ doesn't change to Foo, so you have a problem with SUPER. In short, Don't Do That. Properly written code works properly: `package Base; sub do_me { my $self = shift; print "Base do_me\n"; } package Derived; @ISA = qw(Base); sub do_me { my ($self) = @_; # no shift, so we can goto print "About to jump...\n"; goto &{$self->can("SUPER::do_me")}; } package main; Derived->do_me;` [download] -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply] [d/l]
Re^3: goto superclass method by Aristotle (Chancellor) on Dec 22, 2004 at 21:49 UTC
SUPER:: is always relative to __PACKAGE__, and when you start saying sub Foo::bar, the __PACKAGE__ doesn't change to Foo, so you have a problem with SUPER. That's wrong. `#!/usr/bin/perl use strict; use warnings; package Foo; sub bar { } package Baz; our @ISA = qw( Foo ); sub bar { my $self = shift; print $self->SUPER::can( "bar" ), "\n"; print $self->can( "SUPER::bar" ), "\n"; }; package main; print UNIVERSAL::can( Baz => "bar" ), "\n"; Baz->bar; __END__ CODE(0x815a230) CODE(0x815a230) CODE(0x813bc4c)` [download] Interestingly enough, I thought I had tried the `$self->can( "SUPER::foo" )` combination, but apparently I didn't. Huh. Makeshifts last the longest.	[reply] [d/l]
•Re^4: goto superclass method by merlyn (Sage) on Dec 22, 2004 at 23:19 UTC
Huh? Your example shows that both UNIVERSAL::can and SUPER::can on asking how a "Baz" can "bar" return the same code (which is Baz::bar), and that SUPER::bar for Baz is in fact the one in Foo::bar. That's exactly what I said. You didn't show "wrong" on anything. Did you mean something else? -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re^5: goto superclass method by Aristotle (Chancellor) on Dec 22, 2004 at 23:48 UTC
•Re^6: goto superclass method by merlyn (Sage) on Dec 22, 2004 at 23:53 UTC
Some notes below your chosen depth have not been shown here
Re^3: goto superclass method by steves (Curate) on Dec 22, 2004 at 21:41 UTC
merlyn shows that it takes a wizard to arrive at the purest form of perverted code. Thanks. Now let's all wash our hands. Twice for good measure.	[reply]
Re^4: goto superclass method by Aristotle (Chancellor) on Dec 22, 2004 at 21:50 UTC
I didn't find this perverted at all. What that says about me is your guess. `:-)` Makeshifts last the longest.	[reply]
Re^3: goto superclass method by Mr. Muskrat (Canon) on Dec 22, 2004 at 22:00 UTC
What's wrong with leaving &Derived::do_me out altogether? `package Base; sub do_me { my $self = shift; print "Base do_me\n"; } package Derived; @ISA = qw(Base); package main; Derived->do_me;` [download] It doesn't use goto but the result is the same as far as I can tell. Update: Okay, ignore me. I got distracted from the original question of how to conditionally jump to a super class.	[reply] [d/l]


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