On Fri, 14 Nov 2025 at 17:05, Tomasz Kamiński <[email protected]> wrote:
>
> 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.
"constructing"
OK with that typo fixed, thanks.
> ---
> 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
>
