enhancement type system

[downs]

baleog wrote:
> Can i dream that someday D would has an enhancement type system? To do something like this:
> 
> type T = { int[2..17] | string("default") }

Yay Haskell!

Seriously, the closest AFAIK is 2.0's opDot plus implicit cast .. you could create a type that enforces being between 2 and 17 for as long as possible (as far as type deduction will let it), then falls back to int when an int is needed.

> type U = { T | None };
> 
> or it's a totally bad idea?

2.0's opDot goes towards this direction.

If I understand it correctly, it will let us code like this:

struct NonNull(T) {
  T obj;
  T opDot() {
    debug if (!obj) throw new Exception("Object has somehow become null!");
    return obj;
  }
  T opAssign(T t) {
    if (!t) throw new Exception("Cannot set NonNull to null!");
    obj = t;
  }
}