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

src/util/json/array.h

@@ -31,6 +31,7 @@ public:
 	}
 
 	void emplace_back(Value value);
+	void reserve(size_t size) { m_values.reserve(size); }
 
 	Value& operator[](size_t index);
 

src/util/json/tojson.h

@@ -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.

src/util/json/value.cpp

@@ -19,19 +19,9 @@
 
 namespace Json {
 
-Value::Value(const Value& other)
-{
-	copyFrom(other);
-}
-
-Value& Value::operator=(const Value& other)
+Value::Value(std::nullptr_t)
+	: Value(Type::Null)
 {
-	if (this != &other) {
-		clear();
-		copyFrom(other);
-	}
-
-	return *this;
 }
 
 Value::Value(Type type)
@@ -40,48 +30,6 @@ Value::Value(Type type)
 	create();
 }
 
-Value::Value(bool value)
-	: m_type(Type::Bool)
-{
-	m_value.asBool = value;
-}
-
-Value::Value(int value)
-	: m_type(Type::Number)
-{
-	m_value.asDouble = value;
-}
-
-Value::Value(double value)
-	: m_type(Type::Number)
-{
-	m_value.asDouble = value;
-}
-
-Value::Value(const char* value)
-	: m_type(Type::String)
-{
-	m_value.asString = new std::string(value);
-}
-
-Value::Value(const std::string& value)
-	: m_type(Type::String)
-{
-	m_value.asString = new std::string(value);
-}
-
-Value::Value(const Array& value)
-	: m_type(Type::Array)
-{
-	m_value.asArray = new Array(value);
-}
-
-Value::Value(const Object& value)
-	: m_type(Type::Object)
-{
-	m_value.asObject = new Object(value);
-}
-
 Value::Value(const std::initializer_list<Value>& values)
 {
 	bool isObject = std::all_of(values.begin(), values.end(), [](const Value& value) {
@@ -105,6 +53,23 @@ Value::Value(const std::initializer_list<Value>& values)
 	}
 }
 
+// Copy constructor
+Value::Value(const Value& other)
+{
+	copyFrom(other);
+}
+
+// Assignment operator
+Value& Value::operator=(const Value& other)
+{
+	if (this != &other) {
+		clear();
+		copyFrom(other);
+	}
+
+	return *this;
+}
+
 // ------------------------------------------
 
 Value Value::parse(const std::string& input)

src/util/json/value.h

@@ -12,8 +12,10 @@
 #include <initializer_list>
 #include <iostream> // istream, ostream
 #include <string>
+#include <utility> // forward
 
 #include "util/json/fromjson.h"
+#include "util/json/tojson.h"
 
 namespace Json {
 
@@ -21,6 +23,9 @@ class Array;
 class Object;
 
 class Value {
+private:
+	friend Detail::jsonConstructor;
+
 public:
 	enum class Type {
 		Null,   // null       (case sensitive!)
@@ -31,24 +36,25 @@ public:
 		Object, // {}
 	};
 
-	Value(std::nullptr_t = nullptr) {}
+	// Constructors
+	Value(std::nullptr_t = nullptr);
+	Value(Type type);
+	Value(const std::initializer_list<Value>& values);
+	template<typename T>
+	Value(T value)
+	{
+		toJson(*this, std::forward<T>(value));
+	}
+
+	// Destructor
 	virtual ~Value() { clear(); }
 
 	// Copy constructor
 	Value(const Value& other);
+
 	// Assignment operator
 	Value& operator=(const Value& other);
 
-	Value(Type type);
-	Value(bool value);
-	Value(int value);
-	Value(double value);
-	Value(const char* value);
-	Value(const std::string& value);
-	Value(const Array& value);
-	Value(const Object& value);
-	Value(const std::initializer_list<Value>& values);
-
 	// --------------------------------------
 
 	static Value parse(const std::string& input);