Relocation (= move+destroy)

[Marc Glisse]

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.

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