How to overload operators in a generic class ?

[xiong-pro]

Hi, I wrote a generic class, and try to overload the == operator.

class Foo<T> {
  name: string = '';

  // the value may be string or integer
  constructor(value: T) {
    if (isString<T>()) {
      this.name = value;
    }
    if (isInteger<T>()) {
      this.name = value.toString();
    }
  }

  @operator('==')
  protected eq<U>(right: Foo<U>): bool {
    return this.name == right.name;
  }
}

const f1 = new Foo<string>('abc')
const f2 = new Foo<u32>(123)

if (f1 == f2) {
  // do something ...
}

But it thrown an error.

ERROR AS212: Decorator '@operator' is not valid here.

   @operator('==')
   ~~~~~~~~~~~~~~~

I guess it's because the eq<U>, but don't know how to write the code. 😢

[xiong-pro]

[xiong-pro]

Another question:
I have installed the source-map-support, but still can't see the actual code location in the sources.

[romdotdog]

I do indeed get the AssertionError when trying to compile. Do you see these two TypeScript errors and have you tried to fix them?

[dcodeIO]

Operator overloads cannot be generic. This would work, using two concrete instances of the same type:

  @operator('==')
  protected eq(right: Foo<T>): bool {
    return this.name == right.name;
  }

We certainly need a better error message there, though.

[xiong-pro]

@dcodeIO Thanks for reply. My demand is, the Foo can be instantiated from different types (string and integer), so the operator == should support using two concrete instances of the different type.

[xiong-pro]

@romdotdog yes, I often see these TS errors, and use @ts-ignore comments. 😂

[dcodeIO]

I may misunderstand this, but if you want to compare two Foos both using the same T, then my code snippet above is what you'd do. If you indeed want to compare two Foos of different Ts, then you'd need something like this which cannot be an operator overload because the types are incompatible:

  static hasSameName<T1,T2>(left: Foo<T1>, right: Foo<T2>): bool {
    return left.name == right.name;
  }

[xiong-pro]

@dcodeIO thanks, I have tried this before, but just think overload operators is more pretty ... 🤣

Seeing the bug label, will it be fixed in the future ?

[dcodeIO]

The assertion being hit is a bug, but the limitation is not, at least right now. My fix is linked above, but it only produces a better error message.

[xiong-pro]

@dcodeIO OK, but why not to support it? Seems to work in TS. 😢