vsapsai added inline comments.
================
Comment at: libcxx/include/memory:1470
+ decltype(_VSTD::declval<_Alloc>().construct(_VSTD::declval<_Pointer>(),
+ _VSTD::declval<_Args>())),
+ void
----------------
Quuxplusone wrote:
> 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.
Thanks for the suggestion, Arthur, that worked.
Regarding `_Args` vs `_A0`, I am deliberately using `_Args` because it's not a
manual pseudo-variadic-template expansion and it's not inside
`_LIBCPP_HAS_NO_VARIADICS` block. But I don't feel strong about it, can change
to `_A0`.
https://reviews.llvm.org/D48753
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