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

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source code of libcxx/include/__format/format_context.h