Closures And CoffeeScript's Scoping

The following code defines two functions, lines and circles, that return a function, f and g respectively. Functions f and g are equal (() -> size) only for simplicity, but in g

Solution 1:

You can't use a helper function in your code, as that won't have access to the closure variable as expected. However, you can wrap your whole code in a function so that it returns you the lines or circles function respectively:

make = (def, accessor) ->
    () ->
        size = def
        f = () -> accessor size
        f.size = (_) ->
           size = _
           f
        f

lines = make 10, (size) -> size
circles = make 15, (size) -> size

Solution 2:

You can define a factory function to produce your individual "constructors":

shape = (defaultSize, calculate = (size) -> size) ->
    () ->
        size = defaultSize
        f = () -> calculate size
        f.size = (_) ->
            size = _
            f
        f

lines = shape(10)

circles = shape(15, (size) -> size * size * Math.PI)

This compiles to:

var circles, lines, shape;

shape = function(defaultSize, calculate) {
  if (calculate == null) {
    calculate = function(size) {
      return size;
    };
  }
  return function() {
    var f, size;
    size = defaultSize;
    f = function() {
      return calculate(size);
    };
    f.size = function(_) {
      size = _;
      return f;
    };
    return f;
  };
};

lines = shape(10);

circles = shape(15, function(size) {
  return size * size * Math.PI;
});

console.log(lines()());

console.log(lines().size(20)());

console.log(circles()());

console.log(circles().size(30)());