foreach my $test (@tests){
    if($mask & $byte{$test}){
        if (my $method = $t->can($test)) {
          $mask = $mask ^ $byte{$test} unless $t->$method();
        } # else error handling!
        #if the test returned false we unset the bit
    }
}
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Whenever you have the name of a method and need a coderef, use can(), it will return undef if the object has no such method or a CODE ref otherwise.