When dealing strictly with small positive integers like in your example, an array might be better than a hash.

sub action_1_to_999 {
    print "1 to 999\n";
}

my @dispatch = (
    sub { print "Zero\n" },
    map { \&action_1_to_999 } ( 1 .. 999 ),
    sub { print "1e3\n" },
);

$dispatch[0]->();
$dispatch[23]->();
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