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Re: Relocation (= move+destroy)


On 13/10/18 19:00 +0200, Marc Glisse wrote:
On Sat, 13 Oct 2018, Jonathan Wakely wrote:

On 13/10/18 11:07 +0200, Marc Glisse wrote:
--- libstdc++-v3/include/bits/alloc_traits.h	(revision 265131)
+++ libstdc++-v3/include/bits/alloc_traits.h	(working copy)
@@ -233,38 +233,43 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
	  using type = decltype(__test<_Alloc>(0));
	};

     template<typename _Tp, typename... _Args>
	using __has_construct
	  = typename __construct_helper<_Tp, _Args...>::type;

     template<typename _Tp, typename... _Args>
	static _Require<__has_construct<_Tp, _Args...>>
	_S_construct(_Alloc& __a, _Tp* __p, _Args&&... __args)
+ noexcept(noexcept(__a.construct(__p, std::forward<_Args>(__args)...)))

You could use std::declval<_Args>()... instead of forwarding __args...
which would be slightly shorter (and might keep some of the others on
a single line). No need to change it unless you want to, either is OK.

In order to reduce the risk of bugs, my preference is

1) noexcept(auto): I am amazed that no compiler has implemented it yet, even as a private extension spelled __noexcept_auto or whatever, since it reduces significantly the burden on standard library developers. As a recent example, PR 87538 would never have had a chance to exist.

2) an exact copy-paste of the body of the function.

That's a good enough reason for me. Unless one of us implements
noexcept(auto) in GCC and Clang in the next few days, let's go with
what you have in the patch :-)


3) something else only if needed, for instance because 2) misses the conversion to the result type.

Of course, since there is more chance *you* will have to maintain that mess, whatever style you find easier to maintain is more important.

--
Marc Glisse


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