xref: /llvm-project/libcxx/include/__format/format_context.h (revision c6f3b7bcd0596d30f8dabecdfb9e44f9a07b6e4c) 
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_FORMAT_CONTEXT_H
11 #define _LIBCPP___FORMAT_FORMAT_CONTEXT_H
12 
13 #include <__concepts/same_as.h>
14 #include <__config>
15 #include <__format/buffer.h>
16 #include <__format/format_arg.h>
17 #include <__format/format_arg_store.h>
18 #include <__format/format_args.h>
19 #include <__format/format_error.h>
20 #include <__fwd/format.h>
21 #include <__iterator/back_insert_iterator.h>
22 #include <__iterator/concepts.h>
23 #include <__memory/addressof.h>
24 #include <__utility/move.h>
25 #include <__variant/monostate.h>
26 
27 #if _LIBCPP_HAS_LOCALIZATION
28 #  include <__locale>
29 #  include <optional>
30 #endif
31 
32 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
33 #  pragma GCC system_header
34 #endif
35 
36 _LIBCPP_PUSH_MACROS
37 #include <__undef_macros>
38 
39 _LIBCPP_BEGIN_NAMESPACE_STD
40 
41 #if _LIBCPP_STD_VER >= 20
42 
43 template <class _OutIt, class _CharT>
44   requires output_iterator<_OutIt, const _CharT&>
45 class _LIBCPP_TEMPLATE_VIS basic_format_context;
46 
47 #  if _LIBCPP_HAS_LOCALIZATION
48 /**
49  * Helper to create a basic_format_context.
50  *
51  * This is needed since the constructor is private.
52  */
53 template <class _OutIt, class _CharT>
54 _LIBCPP_HIDE_FROM_ABI basic_format_context<_OutIt, _CharT>
55 __format_context_create(_OutIt __out_it,
56                         basic_format_args<basic_format_context<_OutIt, _CharT>> __args,
57                         optional<std::locale>&& __loc = nullopt) {
58   return std::basic_format_context(std::move(__out_it), __args, std::move(__loc));
59 }
60 #  else
61 template <class _OutIt, class _CharT>
62 _LIBCPP_HIDE_FROM_ABI basic_format_context<_OutIt, _CharT>
63 __format_context_create(_OutIt __out_it, basic_format_args<basic_format_context<_OutIt, _CharT>> __args) {
64   return std::basic_format_context(std::move(__out_it), __args);
65 }
66 #  endif
67 
68 using format_context = basic_format_context<back_insert_iterator<__format::__output_buffer<char>>, char>;
69 #  if _LIBCPP_HAS_WIDE_CHARACTERS
70 using wformat_context = basic_format_context< back_insert_iterator<__format::__output_buffer<wchar_t>>, wchar_t>;
71 #  endif
72 
73 template <class _OutIt, class _CharT>
74   requires output_iterator<_OutIt, const _CharT&>
75 class
76     // clang-format off
77     _LIBCPP_TEMPLATE_VIS
78     _LIBCPP_PREFERRED_NAME(format_context)
79     _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wformat_context))
80     // clang-format on
81     basic_format_context {
82 public:
83   using iterator  = _OutIt;
84   using char_type = _CharT;
85   template <class _Tp>
86   using formatter_type = formatter<_Tp, _CharT>;
87 
88   _LIBCPP_HIDE_FROM_ABI basic_format_arg<basic_format_context> arg(size_t __id) const noexcept {
89     return __args_.get(__id);
90   }
91 #  if _LIBCPP_HAS_LOCALIZATION
92   _LIBCPP_HIDE_FROM_ABI std::locale locale() {
93     if (!__loc_)
94       __loc_ = std::locale{};
95     return *__loc_;
96   }
97 #  endif
98   _LIBCPP_HIDE_FROM_ABI iterator out() { return std::move(__out_it_); }
99   _LIBCPP_HIDE_FROM_ABI void advance_to(iterator __it) { __out_it_ = std::move(__it); }
100 
101 private:
102   iterator __out_it_;
103   basic_format_args<basic_format_context> __args_;
104 #  if _LIBCPP_HAS_LOCALIZATION
105 
106   // The Standard doesn't specify how the locale is stored.
107   // [format.context]/6
108   // std::locale locale();
109   //   Returns: The locale passed to the formatting function if the latter
110   //   takes one, and std::locale() otherwise.
111   // This is done by storing the locale of the constructor in this optional. If
112   // locale() is called and the optional has no value the value will be created.
113   // This allows the implementation to lazily create the locale.
114   // TODO FMT Validate whether lazy creation is the best solution.
115   optional<std::locale> __loc_;
116 
117   template <class _OtherOutIt, class _OtherCharT>
118   friend _LIBCPP_HIDE_FROM_ABI basic_format_context<_OtherOutIt, _OtherCharT> __format_context_create(
119       _OtherOutIt, basic_format_args<basic_format_context<_OtherOutIt, _OtherCharT>>, optional<std::locale>&&);
120 
121   // Note: the Standard doesn't specify the required constructors.
122   _LIBCPP_HIDE_FROM_ABI explicit basic_format_context(
123       _OutIt __out_it, basic_format_args<basic_format_context> __args, optional<std::locale>&& __loc)
124       : __out_it_(std::move(__out_it)), __args_(__args), __loc_(std::move(__loc)) {}
125 #  else
126   template <class _OtherOutIt, class _OtherCharT>
127   friend _LIBCPP_HIDE_FROM_ABI basic_format_context<_OtherOutIt, _OtherCharT>
128       __format_context_create(_OtherOutIt, basic_format_args<basic_format_context<_OtherOutIt, _OtherCharT>>);
129 
130   _LIBCPP_HIDE_FROM_ABI explicit basic_format_context(_OutIt __out_it, basic_format_args<basic_format_context> __args)
131       : __out_it_(std::move(__out_it)), __args_(__args) {}
132 #  endif
133 
134 public:
135   basic_format_context(const basic_format_context&)            = delete;
136   basic_format_context& operator=(const basic_format_context&) = delete;
137 };
138 
139 // A specialization for __retarget_buffer
140 //
141 // See __retarget_buffer for the motivation for this specialization.
142 //
143 // This context holds a reference to the instance of the basic_format_context
144 // that is retargeted. It converts a formatting argument when it is requested
145 // during formatting. It is expected that the usage of the arguments is rare so
146 // the lookups are not expected to be used often. An alternative would be to
147 // convert all elements during construction.
148 //
149 // The elements of the retargets context are only used when an underlying
150 // formatter uses a locale specific formatting or an formatting argument is
151 // part for the format spec. For example
152 //   format("{:256:{}}", input, 8);
153 // Here the width of an element in input is determined dynamically.
154 // Note when the top-level element has no width the retargeting is not needed.
155 template <class _CharT>
156 class _LIBCPP_TEMPLATE_VIS basic_format_context<typename __format::__retarget_buffer<_CharT>::__iterator, _CharT> {
157 public:
158   using iterator  = typename __format::__retarget_buffer<_CharT>::__iterator;
159   using char_type = _CharT;
160   template <class _Tp>
161   using formatter_type = formatter<_Tp, _CharT>;
162 
163   template <class _Context>
164   _LIBCPP_HIDE_FROM_ABI explicit basic_format_context(iterator __out_it, _Context& __ctx)
165       : __out_it_(std::move(__out_it)),
166 #  if _LIBCPP_HAS_LOCALIZATION
167         __loc_([](void* __c) { return static_cast<_Context*>(__c)->locale(); }),
168 #  endif
169         __ctx_(std::addressof(__ctx)),
170         __arg_([](void* __c, size_t __id) {
171           auto __visitor = [&](auto __arg) -> basic_format_arg<basic_format_context> {
172             if constexpr (same_as<decltype(__arg), monostate>)
173               return {};
174             else if constexpr (same_as<decltype(__arg), typename basic_format_arg<_Context>::handle>)
175               // At the moment it's not possible for formatting to use a re-targeted handle.
176               // TODO FMT add this when support is needed.
177               std::__throw_format_error("Re-targeting handle not supported");
178             else
179               return basic_format_arg<basic_format_context>{
180                   __format::__determine_arg_t<basic_format_context, decltype(__arg)>(),
181                   __basic_format_arg_value<basic_format_context>(__arg)};
182           };
183 #  if _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
184           return static_cast<_Context*>(__c)->arg(__id).visit(std::move(__visitor));
185 #  else
186           _LIBCPP_SUPPRESS_DEPRECATED_PUSH
187           return std::visit_format_arg(std::move(__visitor), static_cast<_Context*>(__c)->arg(__id));
188           _LIBCPP_SUPPRESS_DEPRECATED_POP
189 #  endif // _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
190         }) {
191   }
192 
193   _LIBCPP_HIDE_FROM_ABI basic_format_arg<basic_format_context> arg(size_t __id) const noexcept {
194     return __arg_(__ctx_, __id);
195   }
196 #  if _LIBCPP_HAS_LOCALIZATION
197   _LIBCPP_HIDE_FROM_ABI std::locale locale() { return __loc_(__ctx_); }
198 #  endif
199   _LIBCPP_HIDE_FROM_ABI iterator out() { return std::move(__out_it_); }
200   _LIBCPP_HIDE_FROM_ABI void advance_to(iterator __it) { __out_it_ = std::move(__it); }
201 
202 private:
203   iterator __out_it_;
204 
205 #  if _LIBCPP_HAS_LOCALIZATION
206   std::locale (*__loc_)(void* __ctx);
207 #  endif
208 
209   void* __ctx_;
210   basic_format_arg<basic_format_context> (*__arg_)(void* __ctx, size_t __id);
211 };
212 
213 _LIBCPP_CTAD_SUPPORTED_FOR_TYPE(basic_format_context);
214 #endif // _LIBCPP_STD_VER >= 20
215 
216 _LIBCPP_END_NAMESPACE_STD
217 
218 _LIBCPP_POP_MACROS
219 
220 #endif // _LIBCPP___FORMAT_FORMAT_CONTEXT_H
221