unit test for Perl's sort - perl

Question

I try to use a (class) method in an Object for sorting object instances.
package Something;
use strict;
use warnings;
use Data::Dumper;
sub new {
my ($class, $date) = #_;
my $self = bless{}, $class;
$self->{date} = $date;
return $self;
}
sub _sort($$) {
print STDERR Dumper($_[0], $_[1]);
$_[0]->{date} cmp $_[1]->{date};
}
package SomethingTest;
use base 'Test::Class';
use Test::More;
__PACKAGE__->runtests() unless caller;
sub sorting : Test {
my $jan = Something->new("2016-01-01");
my $feb = Something->new("2016-02-01");
my $mar = Something->new("2016-03-01");
is_deeply(
sort Something::_sort [$feb, $mar, $jan],
[$jan, $feb, $mar]);
}
I've seen this snippet in perldoc -f sort, hence the prototype for _sort.
# using a prototype allows you to use any comparison subroutine
# as a sort subroutine (including other package's subroutines)
package other;
sub backwards ($$) { $_[1] cmp $_[0]; } # $a and $b are
# not set here
package main;
#new = sort other::backwards #old;
However, the dumped arguments look odd:
$VAR1 = [
bless( {
'date' => '2016-02-01'
}, 'Something' ),
bless( {
'date' => '2016-03-01'
}, 'Something' ),
bless( {
'date' => '2016-01-01'
}, 'Something' )
];
$VAR2 = [
$VAR1->[2],
$VAR1->[0],
$VAR1->[1]
];
and the test fails with
# Failed test 'sorting died (Not a HASH reference at sort.t line 16.)'
# at sort.t line 25.
Is this just my test setup or can't I have the same objects in these arrays?
What else am I missing?

Answer 1

Your problem isn't with the subroutine you pass to sort(), but in the arguments you pass to is_deeply(). The way you have written it parses like this, if we add some parentheses:
is_deeply(
sort(Something::_sort [$feb, $mar, $jan], [$jan, $feb, $mar] )
);
That is, you're telling sort() to act on a list consisting of two anonymous array references, and then is_deeply() to run with the single argument returned from sort (except it crashes before is_deeply() can try to run and complain that you gave it too few arguments to work with).
This is probably closer to what you intended:
is_deeply(
[sort(Something::_sort ($feb, $mar, $jan))],
[$jan, $feb, $mar]);
That is, tell is_deeply() to compare two anonymous arrays, the first of which is made from telling sort() to apply your sorting routine to the list ($feb, $mar, $jan).