Basic multi dispatch

Multi dispatch allows to overload function names and let the types of its argument to determin which one is actually called.

multi sub twice(Int $x) {
    return $x * 2;

multi sub twice(Str $s) {
    return "$s, $s";

say twice(42); # 84
say twice("hi"); # hi, hi

Here, the two subs with the same name expect arguments of different types, Int and Str, respectively. Thus the call of twice leads to execution of either twice(Int) or twice(Str).

The keyword multi is obligatory to tell the compiler that this sub may be overloaded. Would you omit multi, you will get a compile error Redeclaration of routine twice.