Promises in D

[Calvin P]

On Wednesday, 7 April 2021 at 16:43:59 UTC, Vladimir Panteleev 
wrote:
> Reference counting doesn't change the situation. With 
> delegates, the resource provider can pass a temporary view into 
> an internal buffer owned by the provider. With reference 
> counting, you still need to allocate memory dynamically, and 
> possibly do an additional copy from the internal buffer to the 
> reference-counted one.

I don't think so.

A buffer instance and it' derivative Slice instance can shared 
one refCount pointer.

If the Promise no long need own the Buffer just release the 
refCount.

If Caller finish with the Buffer, just release the refCount.

If the Buffer need be handle by multi callback cross thread, then 
it is passed by const. If callback need modify it then it should 
copy the Slice.

A const temporary view (in my case a const Slice) or a non-const 
temporary view (a Unique Slice) can work with Atomic refCount 
with multi thread safe code.

A Unique Slice will borrow the ownership from Buffer and return 
to Buffer when it released.

If the Buffer refCount is zero when Unique Slice released, the 
resource is release to object pool for reuse.

I don't see a case your Promise solution can void copy Slice but 
refCount need do copy.