On Friday, February 15, 2019 3:06:34 AM MST Kagamin via Digitalmars-d-learn wrote: > Union is just a pretty cast, type system guarantees don't hold > for it.
Well, technically, what's supposed to be the case is that when you cast, the type system guarantees still hold but it's up to the programmer to make sure that they do - just like how it's up to the programmer to ensure that @trusted code is really @safe. Rebindable is a pretty weird case with what it's doing, but I'm pretty sure that it's actually violating the type system with what it does in that you can't rely on the value of the immutable reference itself not being mutated even though it's immutable. The type system guarantees for what the reference refers to are maintained but not the guarantees for the actual reference. In practice, I don't think that it's actually a problem, but in principle, it's violating the type system, and a particularly aggressive optimizer could make a bad assumption. However, given that a union is involved, and as such the "cast" is built into the type, I question that any optimizer would ever make the wrong assumption about Rebindable. - Jonathan M Davis
