Reified classes

[DartBot]

This issue was originally filed by [email protected]

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What steps will reproduce the problem?

The class of an object is not accessible what leads to some shortcomings when implementing the operator == in a class hierarchy (please correct me if I am wrong). For example the following code is rather repetitive and error prone:

class A {
  var a;
  operator == (other) => other is A && a == other.a;
}

class B extends A {
  var b;
  // alternatively we could call super, but that would do unnecessary class checks
  operator == (other) => other is B && a == other.a && b == other.b;
}

class C extends B {
  // alternatively we could call super, but that would do unnecessary class checks
  operator == (other) => other is C && a == other.a && b == other.b;
}

What is the expected output? What do you see instead?

class A {
  var a;
  // access to a comparable class object would simplify the code
  operator == (other) => this.class == other.class && a == other.a;
}

class B extends A {
  var b;
  operator == (other) => super == other && b == other.b;
}

class C extends B {
  // no necessary to implement operator == here
}

What version of the product are you using? On what operating system?

Dart SDK version 7904

[madsager]

Added Area-Language, Triaged labels.

[gbracha]

Set owner to @gbracha.
Added Accepted label.

[gbracha]

I'm renaming this to cover the issue more generally than just the use in equality functions.

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Removed Type-Defect label.
Added Type-Enhancement label.
Changed the title to: "Reified classes".

[gbracha]

It's in the 0.11 spec. Basic idea is that there will be a method on object (probably called type) that produces a suitable token representing the runtime class of the object. The name of a class or type parameter will also serve such a token when used as an expression.

Detailed proposal to be made available soon.

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Added this to the M1 milestone.
Added Done label.