use constant ATTACK_TYPES => [
    {
        type   => 'light',
        damage => 1,
        speed  => 5,
    },
    {
        type   => 'fast',
        damage => 1,
        speed  => 7,
    },
    {
        type   => 'heavy',
        damage => 2,
        speed  => 4,
    },
];

foreach my $attack ( @{ATTACK_TYPES()} ) {
    my $name = "new_$attack->{type}";
    {
        no strict 'refs';
        *{$name} = sub { return shift->new(%$attack) };
    }
}

##</code><code>##

use IO::All;
use JSON 'decode_json';

use constant ATTACK_PARAMS => [ qw/ type damage speed / ];

my $attack_types 
    = decode_json( io('attacks.json')->slurp );

foreach my $attack ( @$attack_types ) {

    exists $attack->{$_} or die "Malformed attack type: $_\n"
        for @{ATTACK_PARAMS()};

    my $name = "new_$attack->{type}";
    {
        no strict 'refs';
        *{$name} = sub { return shift->new(@{$attack}{ATTACK_PARAMS()}) };
    }

}