mirror of
https://github.com/gcc-mirror/gcc.git
synced 2026-05-06 14:59:39 +02:00
e73a6d9827
This implements the library changes in P0849R8 "auto(x): decay-copy in the language" which consist of replacing most uses of the exposition-only function decay-copy with auto(x) throughout the library wording. We implement this as a DR against C++20 since there should be no behavior change in practice (especially in light of LWG 3724 which makes decay-copy SFINAE-friendly). The main difference between decay-copy and auto(x) is that decay-copy materializes its argument unlike auto(x), and so the latter is a no-op when its argument is a prvalue. Effectively the former could introduce an unnecessary move constructor call in some contexts. In C++20 and earlier we could emulate auto(x) with decay_t<decltype((x))>(x). After this paper the only remaining uses of decay-copy in the standard are in the specification of some range adaptors. In our implementation of those range adaptors I believe decay-copy is already implied which is why we don't use __decay_copy explicitly there. So since it's apparently no longer needed this patch goes ahead and removes __decay_copy. libstdc++-v3/ChangeLog: * include/bits/c++config (_GLIBCXX_AUTO_CAST): Define. * include/bits/iterator_concepts.h (_Decay_copy, __decay_copy): Remove. (__member_begin, __adl_begin): Use _GLIBCXX_AUTO_CAST instead of __decay_copy as per P0849R8. * include/bits/ranges_base.h (_Begin): Likewise. (__member_end, __adl_end, _End): Likewise. (__member_rbegin, __adl_rbegin, _RBegin): Likewise. (__member_rend, __adl_rend, _Rend): Likewise. (__member_size, __adl_size, _Size): Likewise. (_Data): Likewise. Reviewed-by: Jonathan Wakely <jwakely@redhat.com>