Copy Constructor DIP

[FeepingCreature]

On Tuesday, 10 July 2018 at 13:38:33 UTC, Jonathan M Davis wrote:
> He thought that it was critical that the invariant be valid 
> when opAssign was called - and there are cases where that's 
> arguably true - but since it doesn't work once you try to do 
> fancier stuff like emplace, I'm of the opinion that invariants 
> are unfortunately a waste of time - even without getting into 
> the issue of init values.
>
> - Jonathan M Davis

moveEmplace bypasses opAssign, since it memcopies directly. 
However, it resets its source value to T.init... so if T.init 
isn't valid, you simply crash whenever the source value goes out 
of scope.

Using types with an invalid T.init feels like playing musical 
chairs with a crash. You can shuffle things around, and make some 
parts work, but *something* is always left crashing at the end.