Detecting Overridden Methods

Ovid has asked for the wisdom of the Perl Monks concerning the following question:

I wanted to check to see if the method I was writing was overriding an existing method in a parent class. That's when I realized that I don't know a truly clean way of doing that. I tried this, but it fails (as it should):

#!/usr/bin/perl -l

use strict;
use warnings;

{
    package A;

    sub foo { 'Whee!' }
    sub check { return shift->SUPER::can('foo') }
}

print A->check->();
[download]

The only thing I can cleanly think of is walking through @ISA, but this seems like such an obvious thing that someone would have solved this.

Cheers,
Ovid

New address of my CGI Course.

Comment on Detecting Overridden Methods Download Code

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Re: Detecting Overridden Methods by ikegami (Patriarch) on Feb 05, 2007 at 16:24 UTC
`package PkgA; use List::Util qw( first ); BEGIN { our @ISA = qw( ... ); } sub foo { 'Whee!' } sub check { return first { $_->can('foo') } @ISA; }` [download]	[reply] [d/l] [select]
Re^2: Detecting Overridden Methods by ikegami (Patriarch) on Feb 05, 2007 at 21:49 UTC
The code in the parent post is neither inheritable nor importable. Fix: `use List::Util qw( first ); sub check { my ($self, $method) = @_; my $class = ref($self) \|\| $self; my $isa = do { no strict 'refs'; \@{$class.'::ISA'} }; return first { $_->can($method) } @$isa; }` [download]	[reply] [d/l]
Re^3: Detecting Overridden Methods by Anonymous Monk on Feb 08, 2007 at 23:58 UTC
Doesn't `use List::Util qw( first );` generate an unwanted `first()` "method" (actually, a function) that is inherited to all children? I would have coded this as `use List::Util ();` and `return List::Util::first { $_->can($method) } @$isa;`.	[reply] [d/l] [select]
Re: Detecting Overridden Methods by diotalevi (Canon) on Feb 05, 2007 at 16:28 UTC
I'd be looking at SUPER's find_parent and find_all_parents methods. Looks like just what you want. ⠤⠤ ⠙⠊⠕⠞⠁⠇⠑⠧⠊	[reply]
Re: Detecting Overridden Methods by Rhandom (Curate) on Feb 05, 2007 at 18:43 UTC
`perl -e 'package B; sub foo {}; sub bar {}; package A; @A::ISA="B"; sub bar {}; sub baz {}; for (qw(foo bar baz)) { print "$_: " .(A->can($_) == B->can($_) ? " same" : " overwritten") ."\n"}'` [download] Prints `foo: same bar: overwritten baz: overwritten` [download] Not sure if that is what you are looking for. my @a=qw(random brilliant braindead); print $a[rand(@a)];	[reply] [d/l] [select]
Re^2: Detecting Overridden Methods by Rhandom (Curate) on Feb 05, 2007 at 18:47 UTC
Ah - I see. You don't want to hard code the classes. My Bad. Then yes - you'll have to look at @A::ISA - but only @A::ISA. `for my $i (@A::ISA) { for (qw(foo bar baz)) { print "$_: " .(A->can($_) == $i->can($_) ? " same" : " overwritten") ."\n"; } }` [download] my @a=qw(random brilliant braindead); print $a[rand(@a)];	[reply] [d/l]
Re: Detecting Overridden Methods by sfink (Deacon) on Feb 05, 2007 at 19:31 UTC
If you know the set of methods you'll need to query, you could check before any of your methods are installed. `package MyPackage; use base "Whatever"; our $can_foo; BEGIN { $can_foo = 1 if MyPackage->can("foo"); } sub foo { 'Whee!' } sub check { return $can_foo; }` [download] Update: But in direct answer to your question, this (surprisingly) seems to work: `MyPackage->can("SUPER::foo")` [download]	[reply] [d/l] [select]
Re^2: Detecting Overridden Methods by ikegami (Patriarch) on Feb 05, 2007 at 19:38 UTC
`our $can_foo;` is not as good as `my $can_foo;` There's no need for a package variable here. `MyPackage->can("foo");` is not as good as `__PACKAGE__->can("foo");` Less redundancy means smaller chance to make an error. I had written this solution before coming up with the one I posted. I couldn't see any advantages to it, so I only included it in my post in comment tags.	[reply] [d/l] [select]