v1/__format/format_context.h

0001 // -*- C++ -*-
0002 //===----------------------------------------------------------------------===//
0003 //
0004 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0005 // See https://llvm.org/LICENSE.txt for license information.
0006 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0007 //
0008 //===----------------------------------------------------------------------===//
0009
0010 #ifndef _LIBCPP___FORMAT_FORMAT_CONTEXT_H
0011 #define _LIBCPP___FORMAT_FORMAT_CONTEXT_H
0012
0013 #include <__concepts/same_as.h>
0014 #include <__config>
0015 #include <__format/buffer.h>
0016 #include <__format/format_arg.h>
0017 #include <__format/format_arg_store.h>
0018 #include <__format/format_args.h>
0019 #include <__format/format_error.h>
0020 #include <__fwd/format.h>
0021 #include <__iterator/back_insert_iterator.h>
0022 #include <__iterator/concepts.h>
0023 #include <__memory/addressof.h>
0024 #include <__utility/move.h>
0025 #include <__variant/monostate.h>
0026
0027 #if _LIBCPP_HAS_LOCALIZATION
0028 #  include <__locale>
0029 #  include <optional>
0030 #endif
0031
0032 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0033 #  pragma GCC system_header
0034 #endif
0035
0036 _LIBCPP_PUSH_MACROS
0037 #include <__undef_macros>
0038
0039 _LIBCPP_BEGIN_NAMESPACE_STD
0040
0041 #if _LIBCPP_STD_VER >= 20
0042
0043 template <class _OutIt, class _CharT>
0044   requires output_iterator<_OutIt, const _CharT&>
0045 class _LIBCPP_TEMPLATE_VIS basic_format_context;
0046
0047 #  if _LIBCPP_HAS_LOCALIZATION
0048 /**
0049  * Helper to create a basic_format_context.
0050  *
0051  * This is needed since the constructor is private.
0052  */
0053 template <class _OutIt, class _CharT>
0054 _LIBCPP_HIDE_FROM_ABI basic_format_context<_OutIt, _CharT>
0055 __format_context_create(_OutIt __out_it,
0056                         basic_format_args<basic_format_context<_OutIt, _CharT>> __args,
0057                         optional<std::locale>&& __loc = nullopt) {
0058   return std::basic_format_context(std::move(__out_it), __args, std::move(__loc));
0059 }
0060 #  else
0061 template <class _OutIt, class _CharT>
0062 _LIBCPP_HIDE_FROM_ABI basic_format_context<_OutIt, _CharT>
0063 __format_context_create(_OutIt __out_it, basic_format_args<basic_format_context<_OutIt, _CharT>> __args) {
0064   return std::basic_format_context(std::move(__out_it), __args);
0065 }
0066 #  endif
0067
0068 using format_context = basic_format_context<back_insert_iterator<__format::__output_buffer<char>>, char>;
0069 #  if _LIBCPP_HAS_WIDE_CHARACTERS
0070 using wformat_context = basic_format_context< back_insert_iterator<__format::__output_buffer<wchar_t>>, wchar_t>;
0071 #  endif
0072
0073 template <class _OutIt, class _CharT>
0074   requires output_iterator<_OutIt, const _CharT&>
0075 class
0076     // clang-format off
0077     _LIBCPP_TEMPLATE_VIS
0078     _LIBCPP_PREFERRED_NAME(format_context)
0079     _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wformat_context))
0080     // clang-format on
0081     basic_format_context {
0082 public:
0083   using iterator  = _OutIt;
0084   using char_type = _CharT;
0085   template <class _Tp>
0086   using formatter_type = formatter<_Tp, _CharT>;
0087
0088   _LIBCPP_HIDE_FROM_ABI basic_format_arg<basic_format_context> arg(size_t __id) const noexcept {
0089     return __args_.get(__id);
0090   }
0091 #  if _LIBCPP_HAS_LOCALIZATION
0092   _LIBCPP_HIDE_FROM_ABI std::locale locale() {
0093     if (!__loc_)
0094       __loc_ = std::locale{};
0095     return *__loc_;
0096   }
0097 #  endif
0098   _LIBCPP_HIDE_FROM_ABI iterator out() { return std::move(__out_it_); }
0099   _LIBCPP_HIDE_FROM_ABI void advance_to(iterator __it) { __out_it_ = std::move(__it); }
0100
0101 private:
0102   iterator __out_it_;
0103   basic_format_args<basic_format_context> __args_;
0104 #  if _LIBCPP_HAS_LOCALIZATION
0105
0106   // The Standard doesn't specify how the locale is stored.
0107   // [format.context]/6
0108   // std::locale locale();
0109   //   Returns: The locale passed to the formatting function if the latter
0110   //   takes one, and std::locale() otherwise.
0111   // This is done by storing the locale of the constructor in this optional. If
0112   // locale() is called and the optional has no value the value will be created.
0113   // This allows the implementation to lazily create the locale.
0114   // TODO FMT Validate whether lazy creation is the best solution.
0115   optional<std::locale> __loc_;
0116
0117   template <class _OtherOutIt, class _OtherCharT>
0118   friend _LIBCPP_HIDE_FROM_ABI basic_format_context<_OtherOutIt, _OtherCharT> __format_context_create(
0119       _OtherOutIt, basic_format_args<basic_format_context<_OtherOutIt, _OtherCharT>>, optional<std::locale>&&);
0120
0121   // Note: the Standard doesn't specify the required constructors.
0122   _LIBCPP_HIDE_FROM_ABI explicit basic_format_context(
0123       _OutIt __out_it, basic_format_args<basic_format_context> __args, optional<std::locale>&& __loc)
0124       : __out_it_(std::move(__out_it)), __args_(__args), __loc_(std::move(__loc)) {}
0125 #  else
0126   template <class _OtherOutIt, class _OtherCharT>
0127   friend _LIBCPP_HIDE_FROM_ABI basic_format_context<_OtherOutIt, _OtherCharT>
0128       __format_context_create(_OtherOutIt, basic_format_args<basic_format_context<_OtherOutIt, _OtherCharT>>);
0129
0130   _LIBCPP_HIDE_FROM_ABI explicit basic_format_context(_OutIt __out_it, basic_format_args<basic_format_context> __args)
0131       : __out_it_(std::move(__out_it)), __args_(__args) {}
0132 #  endif
0133
0134 public:
0135   basic_format_context(const basic_format_context&)            = delete;
0136   basic_format_context& operator=(const basic_format_context&) = delete;
0137 };
0138
0139 // A specialization for __retarget_buffer
0140 //
0141 // See __retarget_buffer for the motivation for this specialization.
0142 //
0143 // This context holds a reference to the instance of the basic_format_context
0144 // that is retargeted. It converts a formatting argument when it is requested
0145 // during formatting. It is expected that the usage of the arguments is rare so
0146 // the lookups are not expected to be used often. An alternative would be to
0147 // convert all elements during construction.
0148 //
0149 // The elements of the retargets context are only used when an underlying
0150 // formatter uses a locale specific formatting or an formatting argument is
0151 // part for the format spec. For example
0152 //   format("{:256:{}}", input, 8);
0153 // Here the width of an element in input is determined dynamically.
0154 // Note when the top-level element has no width the retargeting is not needed.
0155 template <class _CharT>
0156 class _LIBCPP_TEMPLATE_VIS basic_format_context<typename __format::__retarget_buffer<_CharT>::__iterator, _CharT> {
0157 public:
0158   using iterator  = typename __format::__retarget_buffer<_CharT>::__iterator;
0159   using char_type = _CharT;
0160   template <class _Tp>
0161   using formatter_type = formatter<_Tp, _CharT>;
0162
0163   template <class _Context>
0164   _LIBCPP_HIDE_FROM_ABI explicit basic_format_context(iterator __out_it, _Context& __ctx)
0165       : __out_it_(std::move(__out_it)),
0166 #  if _LIBCPP_HAS_LOCALIZATION
0167         __loc_([](void* __c) { return static_cast<_Context*>(__c)->locale(); }),
0168 #  endif
0169         __ctx_(std::addressof(__ctx)),
0170         __arg_([](void* __c, size_t __id) {
0171           auto __visitor = [&](auto __arg) -> basic_format_arg<basic_format_context> {
0172             if constexpr (same_as<decltype(__arg), monostate>)
0173               return {};
0174             else if constexpr (same_as<decltype(__arg), typename basic_format_arg<_Context>::handle>)
0175               // At the moment it's not possible for formatting to use a re-targeted handle.
0176               // TODO FMT add this when support is needed.
0177               std::__throw_format_error("Re-targeting handle not supported");
0178             else
0179               return basic_format_arg<basic_format_context>{
0180                   __format::__determine_arg_t<basic_format_context, decltype(__arg)>(),
0181                   __basic_format_arg_value<basic_format_context>(__arg)};
0182           };
0183 #  if _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
0184           return static_cast<_Context*>(__c)->arg(__id).visit(std::move(__visitor));
0185 #  else
0186           _LIBCPP_SUPPRESS_DEPRECATED_PUSH
0187           return std::visit_format_arg(std::move(__visitor), static_cast<_Context*>(__c)->arg(__id));
0188           _LIBCPP_SUPPRESS_DEPRECATED_POP
0189 #  endif // _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
0190         }) {
0191   }
0192
0193   _LIBCPP_HIDE_FROM_ABI basic_format_arg<basic_format_context> arg(size_t __id) const noexcept {
0194     return __arg_(__ctx_, __id);
0195   }
0196 #  if _LIBCPP_HAS_LOCALIZATION
0197   _LIBCPP_HIDE_FROM_ABI std::locale locale() { return __loc_(__ctx_); }
0198 #  endif
0199   _LIBCPP_HIDE_FROM_ABI iterator out() { return std::move(__out_it_); }
0200   _LIBCPP_HIDE_FROM_ABI void advance_to(iterator __it) { __out_it_ = std::move(__it); }
0201
0202 private:
0203   iterator __out_it_;
0204
0205 #  if _LIBCPP_HAS_LOCALIZATION
0206   std::locale (*__loc_)(void* __ctx);
0207 #  endif
0208
0209   void* __ctx_;
0210   basic_format_arg<basic_format_context> (*__arg_)(void* __ctx, size_t __id);
0211 };
0212
0213 _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(basic_format_context);
0214 #endif // _LIBCPP_STD_VER >= 20
0215
0216 _LIBCPP_END_NAMESPACE_STD
0217
0218 _LIBCPP_POP_MACROS
0219
0220 #endif // _LIBCPP___FORMAT_FORMAT_CONTEXT_H