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// 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 <ios>
#include <memory>
#include <sstream>
#include <string>
#include <tuple>
#include <type_traits>
#include <utility>
#include "base/template_util.h"
#include "base/types/supports_ostream_operator.h"
namespace base {
template <typename... Ts>
std::string ToString(const Ts&... values);
namespace internal {
template <typename T>
concept SupportsToString = requires(const T& t) { t.ToString(); };
// I/O manipulators are function pointers, but should be sent directly to the
// `ostream` instead of being cast to `const void*` like other function
// pointers.
template <typename T>
constexpr bool IsIomanip = false;
template <typename T>
requires(std::derived_from<T, std::ios_base>)
constexpr bool IsIomanip<T&(T&)> = true;
// Function pointers implicitly convert to `bool`, so use this to avoid printing
// function pointers as 1 or 0.
template <typename T>
concept WillBeIncorrectlyStreamedAsBool =
std::is_function_v<std::remove_pointer_t<T>> &&
!IsIomanip<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) {
ss << "[" << sizeof(v) << "-byte object at 0x" << std::addressof(v) << "]";
}
};
// 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);
}
};
// 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. If multiple `values` are given, returns the
// concatenation of the result of applying `ToString` to each value.
template <typename... Ts>
std::string ToString(const Ts&... values) {
std::ostringstream ss;
(...,
internal::ToStringHelper<std::remove_cvref_t<decltype(values)>>::Stringify(
values, ss));
return ss.str();
}
} // namespace base
#endif // BASE_STRINGS_TO_STRING_H_
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