dynamic-dispatch.chpl

/* Dynamic dispatch in Chapel */

{
  /*
     This is not a bug.
     Chapel only support virtual method dispatch, not multiple dispatch
   */
  class A { }

  class B: A { }

  proc f(arg: A) {
    writeln('A version');
  }

  proc f(arg: B) {
    writeln('B version');
  }

  var a  = new A;
  var b = new B;

  f(a); // calls A version
  f(b); // calls B version

  var arr: [1..0] A;
  arr.push_back(b);
  f(arr[1]); // calls A version, even though arr[1] is B
}

{
  /*
     This is not a bug.
     Chapel does not support dynamic dispatch on paren-less methods
   */
  class A {
    proc f {
      writeln('A version');
    }
  }

  class B: A {
    proc f {
      writeln('B version');
    }
  }

  var a  = new A;
  var b = new B;

  a.f; // calls A version
  b.f; // calls B version

  var arr: [1..0] A;
  arr.push_back(b);
  arr[1].f; // calls A version, even though arr[1] is B
}

{
  /* This is an example of dynamic dispatch on an array of base class type */
  class A {
    proc f() {
      writeln('A version');
    }
  }

  class B: A {
    proc f() {
      writeln('B version');
    }
  }

  var a  = new A;
  var b = new B;

  a.f(); // calls A version
  b.f(); // calls B version

  var arr: [1..0] A;
  arr.push_back(b);
  arr[1].f(); // calls B version as expected
}