object_id.t

#!/usr/bin/perl

use v5.10;
use Test::More;

# Can you make this test pass just by changing UNIVERSAL::id and other
# dirty tricks?
#
# You cannot store anything in the object.
# You can make no assumptions about the structure of the object.
# You can not alter or add methods to Foo.
# You can assume 5.10.
# Ideally it should use < O(n) memory (where n is the number of objects created)

{
    package UNIVERSAL;

    # This demonstration is known not to work, references addresses
    # are reused by Perl.
    use Scalar::Util ();
    sub id { Scalar::Util::refaddr $_[0] }
}


# You cannot change anything below this point
{
    package Foo;

    use Scalar::Util qw(refaddr);
    sub new {
        my $class = shift;
        my $string = shift;
        return bless [$string], $class;
    }
    sub set {
        my $self = shift;
        $self->[0] = shift;
    }
    sub DESTROY {}
}

my %seen;
for(1..3) {
    my $obj = Foo->new("wibble");
    my $id = $obj->id;

    # perl will often reuse references
    ok !$seen{$id}, "$id not yet seen";
    $seen{$id}++;

    $obj->set(42);
    is $obj->id, $id, "id not effected by object content";
}


done_testing();