https://bugs.llvm.org/show_bug.cgi?id=44034
Richard Smith <richard-l...@metafoo.co.uk> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |WONTFIX
--- Comment #2 from Richard Smith <richard-l...@metafoo.co.uk> ---
Well, the intent is that you are allowed to pass Args as explicit template
arguments:
algorithm_impl::do_n<Function, Args...>(
std::forward<Function>(func),
std::forward<Args>(args)...,
std::make_integer_sequence<size_t, count>{});
... and in the case where Args is empty, you can instead write that as:
algorithm_impl::do_n<Function>(
std::forward<Function>(func),
std::forward<Args>(args)...,
std::make_integer_sequence<size_t, count>{});
(This specifies Args as an empty pack.)
You can also omit the "Function" in this case, because it's deducible:
algorithm_impl::do_n<>(
std::forward<Function>(func),
std::forward<Args>(args)...,
std::make_integer_sequence<size_t, count>{});
(This still -- presumably! -- specifies Args as an empty pack.)
And finally, [temp.arg.explicit]p4 says you can omit the empty <> in this case
and it means the same thing as including an <>:
algorithm_impl::do_n(std::forward<Function>(func),
std::forward<Args>(args)...,
std::make_integer_sequence<size_t, count>{});
... so by that argument, the code is valid, and MSVC is wrong to reject it, and
Clang and GCC are correct to accept.
This whole area of the C++ standard is underspecified and imprecise, but the
behavior of Clang and GCC here is consistent, reasonable, and in line with
discussions on the C++ committee reflectors about how deduction should work.
MSVC rejects all of the above cases, so I think this is just an MSVC bug. (ICC
has even weirder behavior: it accepts the first two examples but rejects the
last two.)
We're unlikely to make any changes here unless the C++ standard text is
clarified to indicate Clang's behavior is incorrect, so I'm resolving WONTFIX
for now.
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