1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
|
// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_STRINGS_TO_STRING_H_
#define BASE_STRINGS_TO_STRING_H_
#include <concepts>
#include <memory>
#include <sstream>
#include <string>
#include <string_view>
#include <tuple>
#include <type_traits>
#include <utility>
#include "base/base_export.h"
#include "base/containers/span.h"
#include "base/strings/string_view_util.h"
#include "base/types/supports_ostream_operator.h"
#include "base/types/supports_to_string.h"
namespace base {
template <typename T>
std::string ToString(const T& values);
namespace internal {
// Function pointers implicitly convert to `bool`, so use this to avoid printing
// function pointers as "true"/"false".
template <typename T>
concept WillBeIncorrectlyStreamedAsBool =
std::is_function_v<std::remove_pointer_t<T>>;
// Fallback case when there is no better representation.
template <typename T>
struct ToStringHelper {
static void Stringify(const T& v, std::ostringstream& ss) {
// We cast to `void*` to avoid converting a char-like type to char-like*
// which operator<< treats as a string but does not support for multi-byte
// char-like types.
ss << "[" << sizeof(v) << "-byte object at 0x"
<< static_cast<const void*>(std::addressof(v)) << "]";
}
};
// Boolean values. (Handled explicitly so as to not rely on the behavior of
// std::boolalpha.)
template <>
struct ToStringHelper<bool> {
static void Stringify(const bool& v, std::ostringstream& ss) {
ss << (v ? "true" : "false");
}
};
// Most streamables.
template <typename T>
requires(SupportsOstreamOperator<const T&> &&
!WillBeIncorrectlyStreamedAsBool<T>)
struct ToStringHelper<T> {
static void Stringify(const T& v, std::ostringstream& ss) { ss << v; }
};
// Functions and function pointers.
template <typename T>
requires(SupportsOstreamOperator<const T&> &&
WillBeIncorrectlyStreamedAsBool<T>)
struct ToStringHelper<T> {
static void Stringify(const T& v, std::ostringstream& ss) {
ToStringHelper<const void*>::Stringify(reinterpret_cast<const void*>(v),
ss);
}
};
// Integral types that can't stream, like char16_t.
template <typename T>
requires(!SupportsOstreamOperator<const T&> && std::is_integral_v<T>)
struct ToStringHelper<T> {
static void Stringify(const T& v, std::ostringstream& ss) {
if constexpr (std::is_signed_v<T>) {
static_assert(sizeof(T) <= 8);
ss << static_cast<int64_t>(v);
} else {
static_assert(sizeof(T) <= 8);
ss << static_cast<uint64_t>(v);
}
}
};
// Non-streamables that have a `ToString` member.
template <typename T>
requires(!SupportsOstreamOperator<const T&> && SupportsToString<const T&>)
struct ToStringHelper<T> {
static void Stringify(const T& v, std::ostringstream& ss) {
// .ToString() may not return a std::string, e.g. blink::WTF::String.
ToStringHelper<decltype(v.ToString())>::Stringify(v.ToString(), ss);
}
};
// Non-streamable enums (i.e. scoped enums where no `operator<<` overload was
// declared).
template <typename T>
requires(!SupportsOstreamOperator<const T&> && std::is_enum_v<T>)
struct ToStringHelper<T> {
static void Stringify(const T& v, std::ostringstream& ss) {
using UT = typename std::underlying_type_t<T>;
ToStringHelper<UT>::Stringify(static_cast<UT>(v), ss);
}
};
// Tuples. Will recursively apply `ToString()` to each value in the tuple.
template <typename... T>
struct ToStringHelper<std::tuple<T...>> {
template <size_t... I>
static void StringifyHelper(const std::tuple<T...>& values,
std::index_sequence<I...>,
std::ostringstream& ss) {
ss << "<";
(..., (ss << (I == 0 ? "" : ", "), ss << ToString(std::get<I>(values))));
ss << ">";
}
static void Stringify(const std::tuple<T...>& v, std::ostringstream& ss) {
StringifyHelper(v, std::make_index_sequence<sizeof...(T)>(), ss);
}
};
} // namespace internal
// Converts any type to a string, preferring defined operator<<() or ToString()
// methods if they exist.
template <typename T>
std::string ToString(const T& value) {
std::ostringstream ss;
internal::ToStringHelper<std::remove_cvref_t<decltype(value)>>::Stringify(
value, ss);
return ss.str();
}
BASE_EXPORT std::string ToString(std::string_view sv);
BASE_EXPORT std::string ToString(std::u16string_view sv);
BASE_EXPORT std::string ToString(std::wstring_view sv);
namespace to_string_internal {
template <typename T>
concept SpanConvertsToStringView = requires {
{ as_string_view(span<T>()) };
};
} // namespace to_string_internal
// Stringify base::span, hopefully in a way that's useful for tests.
template <typename ElementType, size_t Extent, typename InternalPtrType>
requires(to_string_internal::SpanConvertsToStringView<ElementType> ||
requires(const ElementType& t) {
{ ToString(t) };
})
constexpr std::string ToString(span<ElementType, Extent, InternalPtrType> r) {
std::string out = "[";
if constexpr (to_string_internal::SpanConvertsToStringView<ElementType>) {
const auto sv = as_string_view(r);
using T = std::remove_cvref_t<ElementType>;
if constexpr (std::same_as<wchar_t, T>) {
out += "L\"";
out += ToString(sv);
} else if constexpr (std::same_as<char16_t, T>) {
out += "u\"";
out += ToString(sv);
} else {
out += "\"";
out += sv;
}
out += '\"';
} else if constexpr (Extent != 0) {
// It would be nice to use `JoinString()` here, but making that `constexpr`
// is more trouble than it's worth.
if (!r.empty()) {
out += ToString(r.front());
for (const ElementType& e : r.template subspan<1>()) {
out += ", ";
out += ToString(e);
}
}
}
out += "]";
return out;
}
} // namespace base
#endif // BASE_STRINGS_TO_STRING_H_
|
