Invalid JS: super in constructor shouldn’t accept @params

[ruslux]

This code:

class A
  constructor: (@name) ->
    alert @name, 'name'
    
class B extends A
  constructor: (@name) ->
    super @name

produce wrong code (See class b#super):

var A, B, b;

A = class A {
  constructor(name) {
    this.name = name;
    alert(this.name, 'name');
  }

};

B = class B extends A {
  constructor(name) {
    super(this.name);
    this.name = name;
  }

};

where this is not defined
If I replace @name with name, like here:

class A
  constructor: (@name) ->
    alert @name, 'name'
    
class B extends A
  constructor: (@name) ->
    super name

will produce:

var A, B, b;

A = class A {
  constructor(name1) {
    this.name = name1;
    alert(this.name, 'name');
  }

};

B = class B extends A {
  constructor(name1) {
    super(name);
    this.name = name1;
  }

};

[GeoffreyBooth]

You can't put this before super. ES doesn't allow it.

That said, maybe we should throw an error here? @connec?

[GeoffreyBooth]

@ruslux You want to rewrite your code like this:

class B extends A
  constructor: (name) ->
    super name
    @name = name

I think there’s probably no way for the compiler to do this for you. It would just throw an error, and it would be on you to rewrite your code like the above.

[ruslux]

@GeoffreyBooth It's real code written coffee 1.x. I have tons code like this. Operator @ in args need for reduce this assign hell. * wrathful words *
UPD: Sorry for the aggression, I have a refactoring stress.

[vendethiel]

No need to act so dramatically.
The Coffee 2.x motto is "ES6 integration". That means also forbidding what ES6 forbids.

Probably should error out. Does super((this.name = name, this.name)); work though? (most probably not..)

[connec]

Yup, I'd say it's a bug that super(@) compiles. I might have a chance to look at this in the next day or so.

---

We do also have the option of doing some compiler shenanigans to handle @-params more transparently through rewriting, i.e. compiling:

class B extends A
  constructor: (@name) ->
    super @name
    alert @name

to

class B extends A {
  constructor (name) {
    // Rewrite references to `this.name` prior to `super`
    super(name)
    // Use `this.name` as usual afterwards
    alert(this.name)
  }
}

There are inconsistencies with this though, such as using @ in any other way it wouldn't compile, including an attempt to do something like prop = 'name'; @[prop].

[GeoffreyBooth]

@connec it sounds like the safest thing to do at least for now would be to throw an error? And then if you find some shenanigans that makes this work, we can follow up with that?