Got bit by this - trying to be a bit too clever.

I had a subroutine that was returning a hash - I refactored it so that all the assignments to the hash in the sub happened in a nice clear hash slice operation - however, I found the caller wasn't getting back the right result.

my %run_factors = $this_week->get_run_factors();
...
package Week;
...
sub get_run_factots {
  my ($self) = @_;
  my %run_factors;
  @run_factors{$self->active_runs()} = $self->factors();  
}

[download]
Problem was I was returning the result of the hash slice assignment - which is actually the list on the right hand side of the assignment, not the hash itself. A more minimal example is ... 

#!/usr/bin/perl -w

use strict;

my @keys = qw(a b c d);
my @values = (1, 2, 3, 4);

my %result = build_hash();

use Data::Dumper;
print STDERR Dumper(\%result);

sub build_hash {
    my %return;

    @return{@keys} = @values;
}

[download]
Gives

$VAR1 = {
          '1' => 2,
          '3' => 4
        };

[download]
So beware - dont make the hash assignment be the last thing you do before returning home...

...it is better to be approximately right than precisely wrong. - Warren Buffet

In reply to hash slice ? No thanks, I'm about to return... by leriksen

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