sorting - unit test for Perl's sort -

i try use (class) method in object sorting object instances.

package something;   use strict; use warnings; use data::dumper;  sub new {       ($class, $date) = @_;     $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 {     $jan = something->new("2016-01-01");     $feb = something->new("2016-02-01");     $mar = something->new("2016-03-01");      is_deeply(         sort something::_sort [$feb, $mar, $jan],          [$jan, $feb, $mar]); } 

i've seen snippet in perldoc -f sort, hence prototype _sort.

# using prototype allows use comparison subroutine # sort subroutine (including other package's subroutines) package other; sub backwards ($$) { $_[1] cmp $_[0]; }  # $a , $b                                          # not set here package main; @new = sort other::backwards @old; 

however, dumped arguments 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 test fails with

#   failed test 'sorting died (not hash reference @ sort.t line 16.)' #   @ sort.t line 25. 

is test setup or can't have same objects in these arrays? else missing?

your problem isn't subroutine pass sort(), in arguments pass is_deeply(). way have written parses this, if add parentheses:

is_deeply(         sort(something::_sort [$feb, $mar, $jan], [$jan, $feb, $mar] )     ); 

that is, you're telling sort() act on list consisting of 2 anonymous array references, , is_deeply() run single argument returned sort (except crashes before is_deeply() can try run , complain gave few arguments work with).

this closer intended:

is_deeply(           [sort(something::_sort ($feb, $mar, $jan))],           [$jan, $feb, $mar]); 

that is, tell is_deeply() compare 2 anonymous arrays, first of made telling sort() apply sorting routine list ($feb, $mar, $jan).