I imagine it may have to do with the nature of the functions I'm messing with, or my inexperience with the things I'm playing with, but whatever it is, I don't understand it. Here's a boiled-down version of the module that still suffers from the same problem:

package Cheesy;
use strict;
use warnings;
use Exporter;
our (@ISA, @EXPORT_OK);
@ISA = qw(Exporter);
@EXPORT_OK = qw( grep map );

sub grep (&\@) {
   my $code = shift;
   my $ref = shift;
   return CORE::grep &$code, @$ref if defined wantarray;
   @$ref = CORE::grep &$code, @$ref;
}

sub map (&\@) {
   my $code = shift;
   my $ref = shift;
   return CORE::map &$code, @$ref if defined wantarray;
   @$ref = CORE::map &$code, @$ref;
}

1;
[download]

And here's my test program:

#!/usr/bin/perl -w
use strict;
use Cheesy qw(map grep);

my (@foo,  # tested
    @bar); # desired
@foo = (1 .. 5);
map {$_ * 10} @foo;
@bar = (10, 20, 30, 40, 50);
print "@foo\n";
print "Should be: @bar\n";

@foo = (1 .. 5);
Cheesy::map {$_ * 10} @foo;
@bar = (10, 20, 30, 40, 50);
print "@foo\n";
print "Should be: @bar\n";

@foo = qw(fish chicken cheese);
grep {$_ eq 'cheese'} @foo;
@bar = ('cheese');
print "@foo\n";
print "Should be: @bar\n";

@foo = qw(fish chicken cheese);
Cheesy::grep {$_ eq 'cheese'} @foo;
@bar = ('cheese');
print "@foo\n";
print "Should be: @bar\n";
[download]

And my output:

1 2 3 4 5
Should be: 10 20 30 40 50
10 20 30 40 50
Should be: 10 20 30 40 50
fish chicken cheese
Should be: cheese
cheese
Should be: cheese
[download]

Without specifying the package name, it doesn't work. Were I to add one of the unary ops, though (say, uc), it would. This makes no sense to me, but then again, many things in life don't. So I ask you all - what's going on here? And how can I get this to work the way I want to? Or can I?

His Royal Cheeziness