use strict;
use Data::Dumper;

my $weapons_ref = {
    dagger => { cost => 8, damage => 4, armor => 0 },
    shortsword => { cost => 10, damage => 5, armor => 0 },
    warhammer => { cost => 25, damage => 6, armor => 0 },
    longsword => { cost => 40, damage => 7, armor => 0 },
    greataxe => { cost => 74, damage => 8, armor => 0 },
  };

my $sum_result;
my @sum_fields = qw/cost damage armor/;

map { 
  my $name = $_;
  map { $sum_result->{$_} += $weapons_ref->{$name}->{$_} } @sum_fields
} keys %{ $weapons_ref };

print Dumper($sum_result);