Re: opCast / operator overloading with additional template arguments

[Ali Çehreli via Digitalmars-d-learn]

On 1/10/21 5:09 PM, Paul wrote:

> I'll paste more of my file, I hope that's ok.
Not only ok but much appreciated. :)

>>     T opCast(T)() const if (is(T : Vec!(size, S2), S2)) {

The is expression can be so complicated that I used a different approach 
below. I left notes in capital letters below. Especially cast(S2) looks 
wrong to me:

import std;

version (HoekjeD_Double) {
  private alias standard_accuracy = double;
} else {
  private alias standard_accuracy = float;
}

struct Vec(int size, S = standard_accuracy) {
  // You could add this instead of getting the type from
  // 'content' as in how S2 is aliased in opCast below:
  //
  // alias AccuracyType = S;

  union {
    S[size] content;
    static if (size >= 1) {
      struct {
        S x;
        static if (size >= 2) {
          S y;
          static if (size >= 3) {
            S z;
            static if (size >= 4)
              S w;
          }
        }
      }
    }
  }

  T opCast(T)() const
  // CHANGED:
  if (isInstanceOfVec!T &&
      T.init.content.length == size) {
    // ADDED:
    alias S2 = typeof(T.init.content[0]);
    T converted;
    static foreach (i; 0 .. size)
      // OBSERVATION: Should the cast below be S?
      converted.content[i] = cast(S2) content[i];
    return converted;
  }
}

enum isInstanceOfVec(T) = isInstanceOf!(Vec, T);

void main() {
  auto a = Vec!(42, float)();
  auto b = a.to!(Vec!(42, double));
}

Ali