Try to get rid of std::variant in json_container.hpp

include/util/json_container.hpp

@@ -91,32 +91,163 @@ struct Null
 };
 
 /**
- * Typed Value sum-type implemented as a variant able to represent tree-like JSON structures.
+ * Typed Object.
  *
- * Dispatch on its type by either by using apply_visitor or its get function.
+ * Unwrap the key-value pairs holding type via its values member attribute.
  */
-using Value = std::variant<String, Number, Object, Array, True, False, Null>;
+struct Object;
 
 /**
- * Typed Object.
+ * Typed Array.
  *
- * Unwrap the key-value pairs holding type via its values member attribute.
+ * Unwrap the Value holding type via its values member attribute.
  */
+struct Array;
+
+struct Value;
+
+// Definitions of Object and Array (must come after Value is defined)
 struct Object
 {
     std::unordered_map<std::string, Value> values;
 };
 
-/**
- * Typed Array.
- *
- * Unwrap the Value holding type via its values member attribute.
- */
 struct Array
 {
     std::vector<Value> values;
 };
 
+struct Value
+{
+    enum class Type
+    {
+        Invalid,
+        String,
+        Number,
+        Object,
+        Array,
+        True,
+        False,
+        Null
+    };
+    String string;
+    Number number;
+    Object object;
+    Array array;
+    Type type;
+
+    Value() noexcept : type(Type::Invalid) {}
+    Value(const Null &) noexcept : type(Type::Null) {}
+    Value(const True &) noexcept : type(Type::True) {}
+    Value(const False &) noexcept : type(Type::False) {}
+    Value(String &&string_) noexcept : string(std::move(string_)), type(Type::String) {}
+    Value(Number &&number_) noexcept : number(number_), type(Type::Number) {}
+    Value(Object &&object_) noexcept : object(std::move(object_)), type(Type::Object) {}
+    Value(Array &&array_) noexcept : array(std::move(array_)), type(Type::Array) {}
+    Value(const String &string_) noexcept : string(string_), type(Type::String) {}
+    Value(const Number &number_) noexcept : number(number_), type(Type::Number) {}
+    Value(const Object &object_) noexcept : object(object_), type(Type::Object) {}
+    Value(const Array &array_) noexcept : array(array_), type(Type::Array) {}
+
+    Value(double number) noexcept : number(number), type(Type::Number) {}
+    Value(std::string string) noexcept : string(std::move(string)), type(Type::String) {}
+    Value(const char *string) noexcept : string(string), type(Type::String) {}
+};
+
 } // namespace osrm::util::json
 
+namespace std
+{
+template <typename T> inline T &get(osrm::util::json::Value &value) noexcept;
+
+template <>
+inline osrm::util::json::String &
+get<osrm::util::json::String>(osrm::util::json::Value &value) noexcept
+{
+    return value.string;
+}
+
+template <>
+inline osrm::util::json::Number &
+get<osrm::util::json::Number>(osrm::util::json::Value &value) noexcept
+{
+    return value.number;
+}
+
+template <>
+inline osrm::util::json::Object &
+get<osrm::util::json::Object>(osrm::util::json::Value &value) noexcept
+{
+    return value.object;
+}
+
+template <>
+inline osrm::util::json::Array &
+get<osrm::util::json::Array>(osrm::util::json::Value &value) noexcept
+{
+    return value.array;
+}
+
+template <typename T> inline const T &get(const osrm::util::json::Value &value) noexcept;
+
+template <>
+inline const osrm::util::json::String &
+get<osrm::util::json::String>(const osrm::util::json::Value &value) noexcept
+{
+    return value.string;
+}
+
+template <>
+inline const osrm::util::json::Number &
+get<osrm::util::json::Number>(const osrm::util::json::Value &value) noexcept
+{
+    return value.number;
+}
+
+template <>
+inline const osrm::util::json::Object &
+get<osrm::util::json::Object>(const osrm::util::json::Value &value) noexcept
+{
+    return value.object;
+}
+
+template <>
+inline const osrm::util::json::Array &
+get<osrm::util::json::Array>(const osrm::util::json::Value &value) noexcept
+{
+    return value.array;
+}
+
+template <typename Visitor>
+inline void visit(Visitor &&visitor, const osrm::util::json::Value &value)
+{
+    switch (value.type)
+    {
+    case osrm::util::json::Value::Type::String:
+        visitor(value.string);
+        break;
+    case osrm::util::json::Value::Type::Number:
+        visitor(value.number);
+        break;
+    case osrm::util::json::Value::Type::Object:
+        visitor(value.object);
+        break;
+    case osrm::util::json::Value::Type::Array:
+        visitor(value.array);
+        break;
+    case osrm::util::json::Value::Type::True:
+        visitor(osrm::util::json::True{});
+        break;
+    case osrm::util::json::Value::Type::False:
+        visitor(osrm::util::json::False{});
+        break;
+    case osrm::util::json::Value::Type::Null:
+        visitor(osrm::util::json::Null{});
+        break;
+    case osrm::util::json::Value::Type::Invalid:
+        break;
+    }
+}
+
+} // namespace std
 #endif // JSON_CONTAINER_HPP