Super-type of all function types.

A function value, or an instance of a class with a "call" method, is a subtype of a function type, and as such, a subtype of Function.

abstract class Function {
  /**
   * Dynamically call [function] with the specified arguments.
   *
   * Acts the same as calling function with positional arguments
   * corresponding to the elements of [positionalArguments] and
   * named arguments corresponding to the elements of [namedArguments].
   *
   * This includes giving the same errors if [function] isn't callable or
   * if it expects different parameters.
   *
   * Example: [: Function.apply(foo, [1,2,3], {"f": 4, "g": 5}) :] gives
   * exactly the same result as [: foo(1, 2, 3, f: 4, g: 5) :].
   *
   * If [positionalArguments] is null, it's considered an empty list.
   * If [namedArguments] is omitted or null, it is considered an empty map.
   */
  external static apply(Function function,
                        List positionalArguments,
                        [Map<String,Dynamic> namedArguments]);
}