Promises in D

[Calvin P]

On Thursday, 8 April 2021 at 05:44:15 UTC, Calvin P wrote:
> On Wednesday, 7 April 2021 at 16:43:59 UTC, Vladimir Panteleev 
> wrote:
>> You don't need an object pool at all with delegates. You can 
>> just pass a slice of an array on the stack.
>
> Yes, I cloud just free it.
>
>> The paragraph you quoted discussed delegates, not promises. 
>> Promises do need a copy always, as I stated in my post.
>
> I think it depends on the Promise lifetime and the Caller 
> lifetime.
>
> In my code the buffer do copy at caller lifetime finished like 
> scope exit or __dtor, or it need a bigger capability.
>
> If the Promise outlive the caller lifetime, I can not pass 
> caller delegate as reject/resolve because the caller cloud be 
> destroyed, in this case The callback accepted a copy slice 
> result( when caller destroy the buffer the copy take place).
>
> If you can pass caller delegate to promise(the caller live), 
> then you can pass slice to promise.  If the caller destroy 
> before resolve/reject, then you code crashed or you need copy 
> your template view.
>
> A Buffer destroyed don't mean the memory is released, it can be 
> moved into other instance, or hold by a Slice.

The pointer is If the caller want provide memory to promise pass 
a buffer or slice instead array.  Then the caller can control the 
lifetime of the buffer/slice.

And the buffer always get copy then the buffer/slice lifetime 
finished.

If this in a single thread event loop, then the buffer/slice 
destroy code will make sure the resource will be available for 
the promise object by made a copy.  (or not  copy if the caller 
owned stack array still live when promise resolved/rejected.)