Util: Add flexible constructor toJson() to Json::Value

2022-07-10 00:33:33 +02:00
parent 5c95288874
commit 74dd24a516
4 changed files with 193 additions and 65 deletions
@@ -0,0 +1,156 @@
+/*
+ * Copyright (C) 2022 Riyyi
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#ifndef JSON_TO_JSON_H
+#define JSON_TO_JSON_H
+
+#include <cassert> // assert
+#include <cstddef> // nullptr_t
+#include <map>
+#include <string>
+#include <unordered_map>
+#include <utility> // forward
+
+#include "util/json/array.h"
+#include "util/json/conversion.h"
+#include "util/json/object.h"
+
+namespace Json {
+
+namespace Detail {
+
+struct jsonConstructor {
+	template<typename Json>
+	static void construct(Json& json, bool boolean)
+	{
+		json.clear();
+		json.m_type = Json::Type::Bool;
+		json.m_value.asBool = boolean;
+	}
+
+	template<typename Json>
+	static void construct(Json& json, int number)
+	{
+		json.clear();
+		json.m_type = Json::Type::Number;
+		json.m_value.asDouble = (double)number;
+	}
+
+	template<typename Json>
+	static void construct(Json& json, double number)
+	{
+		json.clear();
+		json.m_type = Json::Type::Number;
+		json.m_value.asDouble = number;
+	}
+
+	template<typename Json>
+	static void construct(Json& json, const char* string)
+	{
+		json.clear();
+		json.m_type = Json::Type::String;
+		json.m_value.asString = new std::string(string);
+	}
+
+	template<typename Json>
+	static void construct(Json& json, const std::string& string)
+	{
+		json.clear();
+		json.m_type = Json::Type::String;
+		json.m_value.asString = new std::string(string);
+	}
+
+	template<typename Json>
+	static void construct(Json& json, const Array& array)
+	{
+		json.clear();
+		json.m_type = Json::Type::Array;
+		json.m_value.asArray = new Array(array);
+	}
+
+	template<typename Json, typename T>
+	static void construct(Json& json, const std::vector<T>& array)
+	{
+		json.clear();
+		json.m_type = Json::Type::Array;
+		json.m_value.asArray = new Array;
+		json.m_value.asArray->reserve(array.size());
+		for (const T& value : array) {
+			json.m_value.asArray->emplace_back(value);
+		}
+	}
+
+	template<typename Json>
+	static void construct(Json& json, const Object& object)
+	{
+		json.clear();
+		json.m_type = Json::Type::Object;
+		json.m_value.asObject = new Object(object);
+	}
+
+	template<typename Json, typename T>
+	static void construct(Json& json, const std::map<std::string, T>& object)
+	{
+		json.clear();
+		json.m_type = Json::Type::Object;
+		json.m_value.asObject = new Object;
+		for (const auto& [name, value] : object) {
+			json.m_value.asObject->emplace(name, value);
+		}
+	}
+
+	template<typename Json, typename T>
+	static void construct(Json& json, const std::unordered_map<std::string, T>& object)
+	{
+		json.clear();
+		json.m_type = Json::Type::Object;
+		json.m_value.asObject = new Object;
+		for (const auto& [name, value] : object) {
+			json.m_value.asObject->emplace(name, value);
+		}
+	}
+};
+
+template<typename Json, typename T>
+void toJson(Json& json, const T& value)
+{
+	jsonConstructor::construct(json, value);
+}
+
+struct toJsonFunction {
+	template<typename Json, typename T>
+	auto operator()(Json& json, T&& value) const
+	{
+		return toJson(json, std::forward<T>(value));
+	}
+};
+
+} // namespace Detail
+
+// Anonymous namespace prevents multiple definition of the reference
+namespace {
+// Function object
+constexpr const auto& toJson = Detail::staticConst<Detail::toJsonFunction>; // NOLINT (misc-definitions-in-headers)
+} // namespace
+
+} // namespace Json
+
+#endif // JSON_TO_JSON_H
+
+// Customization Points
+// https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4381.html
+
+// Json::fromJson is a function object, the type of which is
+// Json::Detail::fromJsonFunction. In the Json::Detail namespace are the
+// fromJson free functions. The function call operator of fromJsonFunction makes
+// an unqualified call to fromJson which, since it shares the Detail namespace
+// with the fromJson free functions, will consider those in addition to any
+// overloads that are found by argument-dependent lookup.
+
+// Variable templates are linked externally, therefor every translation unit
+// will see the same address for Detail::staticConst<Detail::fromJsonFunction>.
+// Since Json::fromJson is a reference to the variable template, it too will
+// have the same address in all translation units.