5.11.3 Rest arguments

Rest arguments allow one to write functions that take a variable number of arguments:

// This function sums its arguments.
int sum(... int[] nums) {
  int total=0; 
  for(int i=0; i < nums.length; ++i)
    total += nums[i];
  return total;
}

sum(1,2,3,4);                       // returns 10
sum();                              // returns 0

// This function subtracts subsequent arguments from the first.
int subtract(int start ... int[] subs) {
  for(int i=0; i < subs.length; ++i)
    start -= subs[i];
  return start;
}

subtract(10,1,2);                   // returns 7
subtract(10);                       // returns 10
subtract();                         // illegal

Putting an argument into a rest array is called packing. One can give an explicit list of arguments for the rest argument, so subtract could alternatively be implemented as

int subtract(int start ... int[] subs) {
  return start - sum(... subs);
}

One can even combine normal arguments with rest arguments:

sum(1,2,3 ... new int[] {4,5,6});   // returns 21

This builds a new six-element array that is passed to sum as nums. The opposite operation, unpacking, is not allowed:

subtract(... new int[] {10, 1, 2});

is illegal, as the start formal is not matched.

If no arguments are packed, then a zero-length array (as opposed to null) is bound to the rest parameter. Note that default arguments are ignored for rest formals and the rest argument is not bound to a keyword.

The overloading resolution in Asymptote is similar to the function matching rules used in C++. Every argument match is given a score. Exact matches score better than matches with casting, and matches with formals (regardless of casting) score better than packing an argument into the rest array. A candidate is maximal if all of the arguments score as well in it as with any other candidate. If there is one unique maximal candidate, it is chosen; otherwise, there is an ambiguity error.

int f(path g);
int f(guide g);
f((0,0)--(100,100)); // matches the second; the argument is a guide

int g(int x, real y);
int g(real x, int x);

g(3,4); // ambiguous; the first candidate is better for the first argument,
        // but the second candidate is better for the second argument

int h(... int[] rest);
int h(real x ... int[] rest);

h(1,2); // the second definition matches, even though there is a cast,
        // because casting is preferred over packing

int i(int x ... int[] rest);
int i(real x, real y ... int[] rest);

i(3,4); // ambiguous; the first candidate is better for the first argument,
        // but the second candidate is better for the second one