I've been asked recently how to tell which perl module overrides a function. Here's an exapmle I managed to write. It's incomplete and most certainly buggy, but I don't think the task in question is worth a full-blown CPAN module anyway. 
#!/usr/bin/perl -w

use strict;

BEGIN {
use Guard;
use Carp;
{
  my $guard = guard { Carp::cluck "Function replaced!" };
  my $code = \&time;
  *time = sub { return $code->(@_); undef $guard; };
};
};

BEGIN { print time(), "\n"; };

use Time::HiRes qw(time);

print time, "\n";
I welcome critique on this one.

Replies are listed 'Best First'.
Re: Find out who redefined a subroutine
by tobyink (Canon) on Jan 25, 2013 at 15:33 UTC

    Ta da!

    sub sub::source {
    require Sub::Identify;
    my ($class, $func) = @_;
    my $code = $class->can($func) or return;
    return Sub::Identify::stash_name($code);
}

{
    package MyApp;
    use Time::HiRes qw(time);
    use Carp;
}

# Where do MyApp's subs come from?
#
print MyApp->sub::source('carp'), "\n";
print MyApp->sub::source('time'), "\n";

# Where do Carp's subs come from?
#
print Carp->sub::source('carp'), "\n";
print Carp->sub::source('import'), "\n";

    [download]

    Though it's worth noting that Sub::Name is able to fool Sub::Identify. Also, Moose/Moo/etc do stringy eval stuff that fools Sub::Identify (deliberately).

    package Cow { use Moo; has name => (is => 'lazy', default => sub { 'Mooington' }) } say Cow->new->name
[reply]
[d/l]
      Aha, so there *is* a full-blown CPAN module for this. Thanks for noting!

      My code can be fooled, too.

      Just copy original subref to a private variable and it would think the sub is still the original one.

[reply]
        Maybe a way to prevent being fooled is to MD5 the sub, and sign it.
[reply]

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