multiple delegation

multiple-delegation.js

var boo = require('boo')


var Delegate = {

  // Makes the given property a getter, that will try the
  // objects in order until it finds a suitable one.
  //
  // proxy :: String → Object
  proxy:
  function proxy(property) {
    var local = "_" + property
    Object.defineProperty(this, property, {
      get:          delegate_property
    , set:          function(value){ this[local] = value }
    , configurable: true
    , enumerable:   true })

    return this

    function delegate_property() { var i
      if (local in this)     return this[local]
      if (!this.proto_list)  return undefined
      i = this.proto_list.length
      while (i--)
        if (property in this.proto_list[i])
          return this.proto_list[i][property] }}
}


var foo = { x: 1, z: 1 }
var bar = { y: 2 }
var baz = boo.clone(Delegate, {
  proto_list: [foo, bar]
, _z: 2
})

baz.proxy('x').proxy('y').proxy('z')

console.log(baz.x, baz.y, baz.z)
// 1 2 2

baz.proto_list = []
console.log(baz.x, baz.y, baz.z)
// undefined undefined 2

baz.proto_list = [foo, bar]
foo.y = 1
console.log(baz.x, baz.y, baz.z)
// 1 2 2   -- bar still has a higher precedence :3