CoffeeScript: Accessing outer class objects from inner class instance

Question

If there any way to access outer class fields from inner class instance, EXCEPT passing outer class instance to inner class constructor?

To be more specific, I have a simple example:

class Test
  constructor: (@number) ->

  class SubTest
    constructor: (@name) ->

    toString: () ->
      console.log @name, @number

  getSubTest: () ->
    return new SubTest "SubTest"

test = new Test 10
test.getSubTest().toString() # SubTest undefined

So, I want to get "SubTest 10" instead of "SubTest undefined". Is it possible?

asawyer · Accepted Answer · 2012-08-27 12:43:00Z

4

Good news! It turns out if you create the closure over @ yourself, it works just fine:

class Test
  self = []
  constructor: (@number) ->
    self = @

  class SubTest
    constructor: (@name) ->

    toString: () ->
      @name + self.number

  getSubTest: () ->
    return new SubTest "SubTest"

test = new Test 10
v = test.getSubTest().toString()

alert v

Translates to :

var Test, test, v;

Test = (function() {
  var SubTest, self;

  self = [];

  function Test(number) {
    this.number = number;
    self = this;
  }

  SubTest = (function() {

    function SubTest(name) {
      this.name = name;
    }

    SubTest.prototype.toString = function() {
      return this.name + self.number;
    };

    return SubTest;

  })();

  Test.prototype.getSubTest = function() {
    return new SubTest("SubTest");
  };

  return Test;

})();

test = new Test(10);

v = test.getSubTest().toString();

alert(v);

Output:

SubTest10

edited Aug 27, 2012 at 12:43

answered Aug 27, 2012 at 12:13

asawyer

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6 Comments

Mariya Davydova Over a year ago

Well, passing number as an argument to constructor is possible solution, of course, but not the one I need. I would like not to pass any additional arguments to inner class constructor, as I need some universal solution, allowing me to access any of possibly big number of outer class fields. However, thank you for the answer.

asawyer Over a year ago

@Leaom The problem is the way coffescript encapsulates the inner class off, so I'm afraid this behavior is by design.

asawyer Over a year ago

@Leaom See my new edit, I think I found a good workaround for you.

Mariya Davydova Over a year ago

Oh, that looks great! I think it perfectly solves my problem. Thanks a lot!

asawyer Over a year ago

I hope an expert like @TrevorBurnham might drop by and offer some further insight or possibly a cleaner solution.

|

pghalliday · Accepted Answer · 2014-12-15 15:23:00Z

1

It's an old question but the accepted answer doesn't work if multiple instances of the outer class are needed (as pointed out by @costa-shapiro). Here is an alternative approach to create the closure with the inner class.

SubTest = (test) ->
  class SubTest
    constructor: (@name) ->

    toString: () =>
      console.log @name, test.number

class Test
  constructor: (@number) ->
    @SubTest = SubTest @

  getSubTest: () =>
    return new @SubTest "SubTest"

test = new Test 10
test.getSubTest().toString()

edited Dec 15, 2014 at 15:23

answered Dec 15, 2014 at 15:11

pghalliday

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