Do you have usecases for opAssign?

[Eugene Wissner]

On Friday, 29 June 2018 at 07:37:46 UTC, FeepingCreature wrote:
> On Friday, 29 June 2018 at 07:31:42 UTC, Eugene Wissner wrote:
>> You can move only exactly the same type. with opAssign you can 
>> assign a differnt type. So opAssign should forward assignment 
>> to the underlying type if you assign nor Nullable!T nor T.
>
> Sorry, that was unclear; I meant to ask for usecases for 
> T::opAssign(T). Maybe the reason to allow this is just that 
> it's a generalization of the actually useful T::opAssign(S), 
> but I want to know if there's a specific usecase for calling 
> specifically T::opAssign(T).

Not an exact answer, but there is a DIP to add kind of move 
constructor to D:
https://github.com/dlang/DIPs/blob/master/DIPs/DIP1014.md

And Andrei mentioned plans to write a DIP to add a copy 
constructor (and maybe deprecate postblit some day, o leave at as 
is).

So yes people have use cases where they have to access the source 
instance (like in T.opAssign(T)).

The first DIP mentions counting of all instances in the 
application, it can be some kind of "intelligent" assignment, 
where you copy/move only some parts of the source instance (and 
not copy/move it completely) or adjusting the internal 
references/structure of the source instance - something like 
this, I think.