[PATCH] D48753: [libcxx] Use custom allocator's `construct` in C++03 when available.

[Volodymyr Sapsai via Phabricator via cfe-commits]

vsapsai added inline comments.


================
Comment at: libcxx/include/memory:1470
+        decltype(_VSTD::declval<_Alloc>().construct(_VSTD::declval<_Pointer>(),
+                                                    _VSTD::declval<_Args>())),
+        void
----------------
Quuxplusone wrote:
> I think you should replace this `)))` with `)), void())` for absolute correctness (e.g. `construct` might plausibly return a pointer to the constructed object, and I think C++03 is okay with that).
> Otherwise, awesome, this looks like what I'd expect. :)
The standard says the result of `construct` is not used but I haven't found any mention it **must** be `void`.

That being said, the proposed change fails for the C++03 macro-based decltype shim:

    error: too many arguments provided to function-like macro invocation
                                        _VSTD::declval<_Args>()), void()),
                                                                  ^

One option to fix that is to use

    is_same
    <
        decltype(_as_before_),
        decltype(_the_same_copy_pasted_argument_)
    >

But I don't think this use case is worth such hacks.


https://reviews.llvm.org/D48753