Re: The relationship of invariants and alias this

[Steven Schveighoffer via Digitalmars-d]

On 11/11/14 6:48 AM, ZombineDev wrote:
AFAIU, even if you had a getter in the alias this:
---
import std.stdio;

struct ValueRestrictedInteger(int lowerBound, int upperBound) {
   int value;
   auto ref get() { return value; }
   alias get this;

   this (int rhs) { value = rhs; }

   invariant() {
     assert (value >= lowerBound && value <= upperBound);
   }

   void forDemonstrationOnly() {}
}
---

It would still not work:

---
unittest {
   ValueRestrictedInteger!(0, 100) x = 0;

   x -= 100; //is probably lowered to something like this:
   // 1) invariant();
   // 2) int* __temp = &x.value; // this is what get() does
   // 3) invariant();
   // 4) *__temp = *temp - 100;

   //...
}
---

Obviously, 4) will not trigger the invariant because it doesn't call any
public functions.

Correct, the only real solution is to wrap with the actual operators and 
opDispatch.

-Steve