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.
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 >>> >>>
