[v3 PATCH] Make stateful allocator propagation more consistent for operator+(basic_string) (P1165R1)

[Jonathan Wakely]

On 07/05/19 12:22 +0100, Jonathan Wakely wrote:
>On 07/05/19 12:01 +0100, Nina Dinka Ranns wrote:
>>Ack. I've put the use of _Alloc_traits::is_always_equal within #if
>>__cplusplus >= 201703L block since it is officially a C++17 feature.
>>Let me know if you think that's an overkill.
>
>Yes, that's overkill, we provide is_always_equal unconditionally from
>C++11 onwards (to avoid ODR violations in code using different -std
>options). Since it's defined fo C++11 we can use it for C++11.
>
>I can remove that #if and test and commit the result for you though,
>no need for another revision of the patch.
>
>>New changelog below. I didn't change the description of
>>operator+(basic_string&&,basic_string&&) as it's still technically
>>always resulting in an allocator from the first parameter.
>
>Yes, that looks fine. Thanks!

I realised that for !_GLIBCXX_USE_CXX11_ABI we can always use the
optimization, because we don't support stateful allocators for the old
std::string ABI. So I adjusted the patch slightly for that.

I've attached what I'll commit.

Tested powerpc64le-linux (old and new ABI), committing to trunk.


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