Re: Virtual opBinary in interface

[mzfhhhh via Digitalmars-d-learn]

On Thursday, 19 December 2024 at 18:49:28 UTC, sfp wrote:
Subject lines says it all, I think... The choice to make binary 
operators implementable only via this `opBinary` template means 
it's unclear how to get virtual operators on an interface. 
E.g., this toy example *does* compile:
```
interface Scalar {
  Scalar opBinary(string op)(Scalar rhs); // wrong
}
class Int : Scalar {
  int i;
  this(int i) { this.i = i; }
  Int opBinary(string op)(Int rhs) if (op == "+") {
    return new Int(i + this.i);
  }
}

void main() {
  Scalar one = new Int(1);
  Scalar two = one + one;
}
```


The template methods in the interface need to be implemented 
within the interface.

https://dlang.org/spec/interface.html#method-bodies

```d
interface Scalar {
    Scalar opBinary(string op)(Scalar rhs) if (op == "+") {
        return add(rhs);
    }

    Scalar add(Scalar rhs);
}


class Int : Scalar {
    int i;
    this(int i) { this.i = i; }

    Scalar add(Scalar rhs) {
    return new Int((cast(Int)rhs).i + this.i);
    }
}

void main() {
    Scalar one = new Int(1);
    Scalar two = one + one;
}
```