Class as_utf_impl

include/boost/parser/detail/text/transcode_view.hpp:728–755

        template<template<class> class View, format Format>
        struct as_utf_impl : stl_interfaces::range_adaptor_closure<as_utf_impl<View, Format>>
        {
#if BOOST_PARSER_DETAIL_TEXT_USE_CONCEPTS
            template<class R>
                requires is_utf_view<std::remove_cvref_t<R>> ||
                         (std::ranges::viewable_range<R> &&
                          can_utf_view<unpacked_range<R>, View>)
#else
            template<typename R>
#endif
            [[nodiscard]] constexpr auto operator()(R && r) const
            {
                using T = detail::remove_cv_ref_t<R>;
                if constexpr (detail::is_empty_view<T>) {
#if BOOST_PARSER_DETAIL_TEXT_USE_CONCEPTS
                    return std::ranges::empty_view<format_to_type_t<Format>>{};
#else
                    return 42; // Never gonna happen.
#endif
                } else if constexpr (is_utf_view<T>) {
                    return View(std::forward<R>(r).base());
                } else if constexpr (detail::is_charn_view<T>) {
                    return View(std::forward<R>(r));
                } else {
                    return View(detail::unpack_range(std::forward<R>(r)));
                }
            }
        };

        template<class T>
        constexpr bool is_utf32_view = false;