Quuxplusone added inline comments.
================
Comment at: libcxx/include/memory:1470
+ decltype(_VSTD::declval<_Alloc>().construct(_VSTD::declval<_Pointer>(),
+ _VSTD::declval<_Args>())),
+ void
----------------
vsapsai wrote:
> 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.
I think the workaround is easier. Try
```
template <class _Alloc, class _Pointer, class _A0>
struct __has_construct<_Alloc, _Pointer, _A0, typename enable_if<
is_same<
decltype((_VSTD::declval<_Alloc>().construct(
_VSTD::declval<_Pointer>(),
_VSTD::declval<_A0>()
), void() )),
void
>::value
>::type> : std::true_type {};
```
i.e. with an extra set of parens to group the argument to the `decltype` macro: `decltype(())` instead of `decltype()`. I also drive-by edited `Args` to `A0`, matching how it's done elsewhere in pseudo-variadic-templates in this file.
https://reviews.llvm.org/D48753