On Fri, 14 Nov 2025 at 18:04, Hewill Kang <[email protected]> wrote: > > Thanks for the explanation. > During my review, I unexpectedly discovered that this UTF_view, which accepts > an input_range, doesn't consider the fact that the input_iterator only > guarantees that it can be moved. It uses copying in many places. > Perhaps we should only accept forward_range. > Or perhaps we should do nothing, since only libstdc++ authors are using it > anyway.
Yeah this is currently only an internal type, it doesn't matter. > > Tomasz Kaminski <[email protected]> 於 2025年11月15日 週六 上午1:58寫道： >> >> >> >> On Fri, Nov 14, 2025 at 6:55 PM Hewill Kang <[email protected]> wrote: >>> >>> LGTM. >>> >>> I know that CTAD wasn't provided due to heavy header considerations. But >>> wouldn't providing CTAD be an enhancement? >>> At least in terms of user convenience. >> >> I care much more about the use of libstdc++ compile time performance, that >> convenience of the >> libstdc++ authors (only people that should use it). If we get official >> Utf_view, it should >> have the deduction guide in place. >>> >>> >>> Tomasz Kamiński <[email protected]> 於 2025年11月15日 週六 上午1:06寫道： >>>> >>>> Previously, _Utf_view accepted any input_range, including >>>> reference-to-array >>>> types like char(&)[2], and stored it as the _M_base member. In such cases, >>>> _Utf_view was not assignable, failing the requirement to be a view >>>> concept. >>>> >>>> This patch addresses the issue by adding the ranges::view constraint to the >>>> second template parameter of _Utf_view, and for clarity renaming it from >>>> _Range to _View. The constructor is also adjusted to accept its argument >>>> by value (views must be O(1) move-constructible). This prevents implicitly >>>> generated CTAD from deducing a reference type. >>>> >>>> This makes _Utf_view consistent with both other standard views and the >>>> wording from P2728R8: Unicode in the Library, Part 1: UTF Transcoding [1]. >>>> >>>> The explicit CTAD from viewable_range is not defined for _Utf_view because >>>> it depends on views::all_t, views::ref_view, and views::owning_view, >>>> which are declared in <ranges>. Consequently, users must explicitly cast >>>> the argument to a view or specify it as a template parameter. >>>> >>>> [1] https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p2728r8.html >>>> >>>> libstdc++-v3/ChangeLog: >>>> >>>> * include/bits/unicode.h (_Utf_view): Rename the template parameter >>>> from _Range to _View and constrain it with ranges::view. >>>> (_Utf_view::_Utf_view): Accept by value instead of rvalue >>>> reference. >>>> * include/std/format (__format::__write_padded): Replace _Utf_view >>>> over const char32_t(&)[1] with span<const char32_t, 1>. >>>> * testsuite/ext/unicode/view.cc: Add checks if specialization >>>> of _Utf_view satisfy view. Wrap arrays into std::span before >>>> cosntructing _Utf_view. >>>> --- >>>> libstdc++-v3/include/bits/unicode.h | 15 ++++++++------- >>>> libstdc++-v3/include/std/format | 2 +- >>>> libstdc++-v3/testsuite/ext/unicode/view.cc | 16 ++++++++++------ >>>> 3 files changed, 19 insertions(+), 14 deletions(-) >>>> >>>> diff --git a/libstdc++-v3/include/bits/unicode.h >>>> b/libstdc++-v3/include/bits/unicode.h >>>> index 44872db4ed6..09f7c2d7bfb 100644 >>>> --- a/libstdc++-v3/include/bits/unicode.h >>>> +++ b/libstdc++-v3/include/bits/unicode.h >>>> @@ -695,13 +695,14 @@ namespace __unicode >>>> friend class _Utf_iterator; >>>> }; >>>> >>>> - template<typename _ToFormat, ranges::input_range _Range> >>>> + template<typename _ToFormat, ranges::input_range _View> >>>> + requires ranges::view<_View> >>>> class _Utf_view >>>> - : public ranges::view_interface<_Utf_view<_ToFormat, _Range>> >>>> + : public ranges::view_interface<_Utf_view<_ToFormat, _View>> >>>> { >>>> - using _Iterator = _Utf_iterator<ranges::range_value_t<_Range>, >>>> - _ToFormat, >>>> ranges::iterator_t<_Range>, >>>> - ranges::sentinel_t<_Range>>; >>>> + using _Iterator = _Utf_iterator<ranges::range_value_t<_View>, >>>> + _ToFormat, ranges::iterator_t<_View>, >>>> + ranges::sentinel_t<_View>>; >>>> >>>> template<typename _Iter, typename _Sent> >>>> constexpr auto >>>> @@ -725,11 +726,11 @@ namespace __unicode >>>> return _Iterator(__last, __last); >>>> } >>>> >>>> - _Range _M_base; >>>> + _View _M_base; >>>> >>>> public: >>>> constexpr explicit >>>> - _Utf_view(_Range&& __r) : _M_base(std::forward<_Range>(__r)) { } >>>> + _Utf_view(_View __r) : _M_base(std::move(__r)) { } >>>> >>>> constexpr auto begin() >>>> { return _M_begin(ranges::begin(_M_base), ranges::end(_M_base)); } >>>> diff --git a/libstdc++-v3/include/std/format >>>> b/libstdc++-v3/include/std/format >>>> index 1102ac8f6e8..f64f35a202e 100644 >>>> --- a/libstdc++-v3/include/std/format >>>> +++ b/libstdc++-v3/include/std/format >>>> @@ -845,7 +845,7 @@ namespace __format >>>> { >>>> // Encode fill char as multiple code units of type _CharT. >>>> const char32_t __arr[1]{ __fill_char }; >>>> - _Utf_view<_CharT, const char32_t(&)[1]> __v(__arr); >>>> + _Utf_view<_CharT, span<const char32_t, 1>> __v(__arr); >>>> basic_string<_CharT> __padstr(__v.begin(), __v.end()); >>>> __padding = __padstr; >>>> while (__l-- > 0) >>>> diff --git a/libstdc++-v3/testsuite/ext/unicode/view.cc >>>> b/libstdc++-v3/testsuite/ext/unicode/view.cc >>>> index 40c8fcf34fb..677a21d8c1f 100644 >>>> --- a/libstdc++-v3/testsuite/ext/unicode/view.cc >>>> +++ b/libstdc++-v3/testsuite/ext/unicode/view.cc >>>> @@ -7,6 +7,10 @@ >>>> namespace uc = std::__unicode; >>>> using namespace std::string_view_literals; >>>> >>>> +static_assert( std::ranges::view<uc::_Utf8_view<std::string_view>> ); >>>> +static_assert( std::ranges::view<uc::_Utf16_view<std::string_view>> ); >>>> +static_assert( std::ranges::view<uc::_Utf32_view<std::string_view>> ); >>>> + >>>> template<std::ranges::range View> >>>> constexpr void >>>> compare(View v, std::basic_string_view<std::ranges::range_value_t<View>> >>>> s) >>>> @@ -87,18 +91,18 @@ test_illformed_utf16() >>>> compare(uc::_Utf16_view(s.substr(0, 1)), r); >>>> compare(uc::_Utf16_view(s.substr(1, 1)), r); >>>> std::array s2{ s[0], s[0] }; >>>> - compare(uc::_Utf16_view(s2), u"\uFFFD\uFFFD"sv); >>>> + compare(uc::_Utf16_view(std::span(s2)), u"\uFFFD\uFFFD"sv); >>>> std::array s3{ s[0], s[0], s[1] }; >>>> - compare(uc::_Utf16_view(s3), u"\uFFFD\N{CLOWN FACE}"sv); >>>> + compare(uc::_Utf16_view(std::span(s3)), u"\uFFFD\N{CLOWN FACE}"sv); >>>> std::array s4{ s[1], s[0] }; >>>> - compare(uc::_Utf16_view(s4), u"\uFFFD\uFFFD"sv); >>>> + compare(uc::_Utf16_view(std::span(s4)), u"\uFFFD\uFFFD"sv); >>>> std::array s5{ s[1], s[0], s[1] }; >>>> - compare(uc::_Utf16_view(s5), u"\uFFFD\N{CLOWN FACE}"sv); >>>> + compare(uc::_Utf16_view(std::span(s5)), u"\uFFFD\N{CLOWN FACE}"sv); >>>> >>>> std::array<char16_t, 2> s6{ 0xDC00, 0xDC01 }; >>>> - compare(uc::_Utf16_view(s6), u"\uFFFD\uFFFD"sv); >>>> + compare(uc::_Utf16_view(std::span(s6)), u"\uFFFD\uFFFD"sv); >>>> std::array<char16_t, 2> s7{ 0xD7FF, 0xDC00 }; >>>> - compare(uc::_Utf16_view(s7), u"\uD7FF\uFFFD"sv); >>>> + compare(uc::_Utf16_view(std::span(s7)), u"\uD7FF\uFFFD"sv); >>>> } >>>> >>>> constexpr void >>>> -- >>>> 2.51.0 >>>>
