How can I check if a Perl scalar holds a reference to a certain subroutine?

Question

In other words, how can I check for coderef "equality"?

The smartmatch operator doesn't work for obvious reasons (would treat it as CODE->(ANY)), but I've included it in the example to show what I'm after:

use strict;
use warnings;
use feature 'say';

sub pick_at_random {

    my %table = @_;
    return ( values %table )[ rand( keys %table ) ];
}

my %lookup = ( A => \&foo,
               B => \&bar,
               C => \&baz );

my $selected = pick_at_random( %lookup );

say $selected ~~ \&foo ? "Got 'foo'" :
    $selected ~~ \&bar ? "Got 'bar'" :
    $selected ~~ \&baz ? "Got 'baz'" :
                         "Got nadda" ;

Answer 1

You can use normal (numeric) equality (==), as is the case with all references:

Perl> $selected == \&foo


Perl> $selected == \&bar


Perl> $selected == \&baz
1

Live in action here

That breaks when the reference is blessed with something that overloads == or 0+ (which is unlikely for coderefs). In that case, you'd compare Scalar::Util::refaddr($selected).

From man perlref:

Using a reference as a number produces an integer representing its storage location in memory. The only useful thing to be done with this is to compare two references numerically to see whether they refer to the same location.

      if ($ref1 == $ref2) {  # cheap numeric compare of references
           print "refs 1 and 2 refer to the same thing\n";
       }