DIP 1014

[Shachar Shemesh]

On 03/10/18 23:25, Stanislav Blinov wrote:
> It *is* true when the type doesn't have a destructor. Extending that to 
> a move hook, it will also be true because destruction will be elided.
> I know what you're talking about, that happens for types that have 
> destructors.

No, destructors have nothing to do with it, as well they shouldn't. The 
whole point of D moving structs around is that no destruction is needed. 
It took me a while to figure out why your program does appear to work. 
At first I thought it was because of inlining, but that was wrong.

The reason your test case works (sometimes, if you don't breath on it 
too heavily) is because the object is actually moved twice. Once when 
returning from the function into the variable, and another when copied 
into opAssign's argument. This results in it returning to its original 
address.

If you do *anything* to that program, and that includes even changing 
its compilation flags (try enabling inlining), it will stop working.

You should have known that when you found out it doesn't work on ldc: 
ldc and dmd use the same front-end. If you think something works 
fundamentally different between the two, you are probably wrong.

To verify my guess is right, I tried the following change: add to 
createCounter and createCounterNoNRV in your original program (no 
destructors) the following two lines:
   int a;
   write(a);

You have added another local variable to the functions, but otherwise 
changed absolutely nothing. You will notice your program now has an offset.

Shachar