[libcxx-commits] [libcxx] [libc++] LWG3187: P0591R4 reverted DR 2586 fixes to `scoped_allocator_adaptor::construct()` (PR #152424)

[A. Jiang via libcxx-commits]

frederick-vs-ja wrote:

> > > I think we should rather modify the utilities to have the required behaviour in C++17.
> > 
> > 
> > Oh, for `scoped_allocator_adaptor` we need the mechanisms working in C++11 mode. It would be quite non-trivial to rework them for C++11, as (at least) Clang doesn't seem to accept using deduced return types in C++11 mode.
> 
> Urgh. WDYT about implementing the `polymorphic_allocator` part first and then we can see how big the diff would be for C++11?

`polymorphic_allocator` can be hugely simplified. But the situation for `scoped_allocator_adaptor` is quite complicated.

https://github.com/llvm/llvm-project/pull/152424