Even more fun (but less efficient) than this would be to just make the function recursive.

sub add_two
{
    my @in_values = @_;
    if( wantarray )
    {
        #must use +0 to force scalar
        #otherwise we get deep recursion
        return map add_two( $_ ) + 0, @in_values;
    }
    else
    {
        return $in_value[0] + 2;
    }
}
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