Warning: {closure}(): Argument #1 ($a) must be passed by reference, value given in %s on line %d

Warning: {closure}(): Argument #2 ($b) must be passed by reference, value given in %s on line %d

Warning: {closure}(): Argument #1 ($a) must be passed by reference, value given in %s on line %d

Warning: {closure}(): Argument #2 ($b) must be passed by reference, value given in %s on line %d

Warning: {closure}(): Argument #1 ($a) must be passed by reference, value given in %s on line %d

Warning: {closure}(): Argument #2 ($b) must be passed by reference, value given in %s on line %d
int(6)