Dynamic and chainable read only models in coffee-script.

model.coffee

extend = (object, properties) ->
  for key, val of properties
    object[key] = val
  object

merge = (options, overrides) ->
  extend (extend {}, options), overrides

class Model
  field: (name) ->
    @fields ?= []
    @fields.push(name)
    @constructor::[name] = () ->
      if arguments.length == 0
        @attributes[name]
      else
        a = {}
        a[name] = arguments[0]
        a = merge(@attributes,a)
        return new @constructor(a)

class Task2 extends Model
  constructor: (@attributes) ->
    @field "desc"

class Task3 extends Model
  constructor: (@attributes) ->
    @field "desc3"
    
t = new Task2("desc":"ASDFG")
t2 = t
console.log(t.desc(), t.desc() == t2.desc())
console.log(t.desc(), t.desc() == "ASDFG")
t3 = t.desc("ASDF")
console.log(t2.desc(), t2.desc() == "ASDFG")
console.log(t.desc(), t.desc() == "ASDFG")
console.log(t3.desc(), t3.desc() == "ASDF")

tx = new Task3("desc3":"X")

console.log(t2.desc(), t2.desc() == "ASDFG")
console.log(t.desc(), t.desc() == "ASDFG")
console.log(t3.desc(), t3.desc() == "ASDF")
console.log(tx.desc3(), tx.desc3() == "X")
console.log(tx.desc, tx.desc == undefined)
console.log(t2.desc3, t2.desc3 == undefined)
console.log(t.desc3, t.desc3 == undefined)
console.log(t3.desc3, t3.desc3 == undefined)

output.txt

ASDFG true
ASDFG true
ASDFG true
ASDFG true
ASDF true
ASDFG true
ASDFG true
ASDF true
X true
undefined true
undefined true
undefined true
undefined true