libcxx/include/__format/formatter_tuple.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___FORMAT_FORMATTER_TUPLE_H
  11 #define _LIBCPP___FORMAT_FORMATTER_TUPLE_H
  12
  13 #include <__algorithm/ranges_copy.h>
  14 #include <__chrono/statically_widen.h>
  15 #include <__config>
  16 #include <__format/buffer.h>
  17 #include <__format/concepts.h>
  18 #include <__format/format_context.h>
  19 #include <__format/format_error.h>
  20 #include <__format/format_parse_context.h>
  21 #include <__format/formatter.h>
  22 #include <__format/formatter_output.h>
  23 #include <__format/parser_std_format_spec.h>
  24 #include <__type_traits/remove_cvref.h>
  25 #include <__utility/integer_sequence.h>
  26 #include <__utility/pair.h>
  27 #include <string_view>
  28 #include <tuple>
  29
  30 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  31 #  pragma GCC system_header
  32 #endif
  33
  34 _LIBCPP_BEGIN_NAMESPACE_STD
  35
  36 #if _LIBCPP_STD_VER >= 23
  37
  38 template <__fmt_char_type _CharT, class _Tuple, formattable<_CharT>... _Args>
  39 struct _LIBCPP_TEMPLATE_VIS __formatter_tuple {
  40   _LIBCPP_HIDE_FROM_ABI constexpr void set_separator(basic_string_view<_CharT> __separator) noexcept {
  41     __separator_ = __separator;
  42   }
  43   _LIBCPP_HIDE_FROM_ABI constexpr void
  44   set_brackets(basic_string_view<_CharT> __opening_bracket, basic_string_view<_CharT> __closing_bracket) noexcept {
  45     __opening_bracket_ = __opening_bracket;
  46     __closing_bracket_ = __closing_bracket;
  47   }
  48
  49   template <class _ParseContext>
  50   _LIBCPP_HIDE_FROM_ABI constexpr typename _ParseContext::iterator parse(_ParseContext& __ctx) {
  51     auto __begin = __parser_.__parse(__ctx, __format_spec::__fields_tuple);
  52
  53     auto __end = __ctx.end();
  54     // Note 'n' is part of the type here
  55     if (__parser_.__clear_brackets_)
  56       set_brackets({}, {});
  57     else if (__begin != __end && *__begin == _CharT('m')) {
  58       if constexpr (sizeof...(_Args) == 2) {
  59         set_separator(_LIBCPP_STATICALLY_WIDEN(_CharT, ": "));
  60         set_brackets({}, {});
  61         ++__begin;
  62       } else
  63         std::__throw_format_error("Type m requires a pair or a tuple with two elements");
  64     }
  65
  66     if (__begin != __end && *__begin != _CharT('}'))
  67       std::__throw_format_error("The format specifier should consume the input or end with a '}'");
  68
  69     __ctx.advance_to(__begin);
  70
  71     // [format.tuple]/7
  72     //   ... For each element e in underlying_, if e.set_debug_format()
  73     //   is a valid expression, calls e.set_debug_format().
  74     std::__for_each_index_sequence(make_index_sequence<sizeof...(_Args)>(), [&]<size_t _Index> {
  75       auto& __formatter = std::get<_Index>(__underlying_);
  76       __formatter.parse(__ctx);
  77       // Unlike the range_formatter we don't guard against evil parsers. Since
  78       // this format-spec never has a format-spec for the underlying type
  79       // adding the test would give additional overhead.
  80       std::__set_debug_format(__formatter);
  81     });
  82
  83     return __begin;
  84   }
  85
  86   template <class _FormatContext>
  87   typename _FormatContext::iterator _LIBCPP_HIDE_FROM_ABI
  88   format(conditional_t<(formattable<const _Args, _CharT> && ...), const _Tuple&, _Tuple&> __tuple,
  89          _FormatContext& __ctx) const {
  90     __format_spec::__parsed_specifications<_CharT> __specs = __parser_.__get_parsed_std_specifications(__ctx);
  91
  92     if (!__specs.__has_width())
  93       return __format_tuple(__tuple, __ctx);
  94
  95     // The size of the buffer needed is:
  96     // - open bracket characters
  97     // - close bracket character
  98     // - n elements where every element may have a different size
  99     // - (n -1) separators
 100     // The size of the element is hard to predict, knowing the type helps but
 101     // it depends on the format-spec. As an initial estimate we guess 6
 102     // characters.
 103     // Typically both brackets are 1 character and the separator is 2
 104     // characters. Which means there will be
 105     //   (n - 1) * 2 + 1 + 1 = n * 2 character
 106     // So estimate 8 times the range size as buffer.
 107     __format::__retarget_buffer<_CharT> __buffer{8 * tuple_size_v<_Tuple>};
 108     basic_format_context<typename __format::__retarget_buffer<_CharT>::__iterator, _CharT> __c{
 109         __buffer.__make_output_iterator(), __ctx};
 110
 111     __format_tuple(__tuple, __c);
 112
 113     return __formatter::__write_string_no_precision(basic_string_view{__buffer.__view()}, __ctx.out(), __specs);
 114   }
 115
 116   template <class _FormatContext>
 117   _LIBCPP_HIDE_FROM_ABI typename _FormatContext::iterator __format_tuple(auto&& __tuple, _FormatContext& __ctx) const {
 118     __ctx.advance_to(std::ranges::copy(__opening_bracket_, __ctx.out()).out);
 119
 120     std::__for_each_index_sequence(make_index_sequence<sizeof...(_Args)>(), [&]<size_t _Index> {
 121       if constexpr (_Index)
 122         __ctx.advance_to(std::ranges::copy(__separator_, __ctx.out()).out);
 123       __ctx.advance_to(std::get<_Index>(__underlying_).format(std::get<_Index>(__tuple), __ctx));
 124     });
 125
 126     return std::ranges::copy(__closing_bracket_, __ctx.out()).out;
 127   }
 128
 129   __format_spec::__parser<_CharT> __parser_{.__alignment_ = __format_spec::__alignment::__left};
 130
 131 private:
 132   tuple<formatter<remove_cvref_t<_Args>, _CharT>...> __underlying_;
 133   basic_string_view<_CharT> __separator_       = _LIBCPP_STATICALLY_WIDEN(_CharT, ", ");
 134   basic_string_view<_CharT> __opening_bracket_ = _LIBCPP_STATICALLY_WIDEN(_CharT, "(");
 135   basic_string_view<_CharT> __closing_bracket_ = _LIBCPP_STATICALLY_WIDEN(_CharT, ")");
 136 };
 137
 138 template <__fmt_char_type _CharT, formattable<_CharT>... _Args>
 139 struct _LIBCPP_TEMPLATE_VIS formatter<pair<_Args...>, _CharT>
 140     : public __formatter_tuple<_CharT, pair<_Args...>, _Args...> {};
 141
 142 template <__fmt_char_type _CharT, formattable<_CharT>... _Args>
 143 struct _LIBCPP_TEMPLATE_VIS formatter<tuple<_Args...>, _CharT>
 144     : public __formatter_tuple<_CharT, tuple<_Args...>, _Args...> {};
 145
 146 #endif //_LIBCPP_STD_VER >= 23
 147
 148 _LIBCPP_END_NAMESPACE_STD
 149
 150 #endif // _LIBCPP___FORMAT_FORMATTER_TUPLE_H