119 lines
3.4 KiB
C++
119 lines
3.4 KiB
C++
// SPDX-License-Identifier: MIT
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// Copyright (c) 2026 Dim Himro
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#ifndef TYPEFACTORY_H
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#define TYPEFACTORY_H
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#include <memory>
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#include <type_traits>
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#include <unordered_map>
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#include <utility> // std::move
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/**
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* @brief Registry-based factory for creating objects by runtime identifier.
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*
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* Allows registering derived types and instantiating them using a ClassId key.
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*
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* Notes:
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* - Not thread-safe. Register types during initialization phase only.
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* - Re-registering the same id overwrites the previous entry ("last wins").
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* - ClassId must be hashable (std::hash<ClassId> specialization must exist).
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*
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* @tparam ClassId -Unique class identifier type (e.g. std::string, int, enum).
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* @tparam BaseClass -Base type for all created objects.
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* @tparam Arg - Constructor arguments forwarded to registered derived types (by value).
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*
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* Usage example:
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* @code
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* #include <string>
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*
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* struct Base {
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* virtual ~Base() = default;
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* virtual int get() = 0;
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* };
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*
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* struct Derived1 : Base {
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* explicit Derived1(int start) : m_start(start) {}
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* int get() override { return m_start + 1; }
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* int m_start = 0;
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* };
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*
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* struct Derived2 : Base {
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* explicit Derived2(int start) : m_start(start) {}
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* int get() override { return m_start + 2; }
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* int m_start = 0;
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* };
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*
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* TypeFactory<std::string, Base, int> factory;
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* factory.registerType<Derived1>("one");
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* factory.registerType<Derived2>("two");
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*
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* auto a = factory.create("one", 10);
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* auto b = factory.creator("two")(10); // advanced API: get creator function
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*
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* (void)a->get();
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* (void)b->get();
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* @endcode
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*/
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template <class ClassId, class BaseClass, class... Args>
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class TypeFactory {
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public:
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using BasePtr = std::shared_ptr<BaseClass>;
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using CreatorFn = BasePtr (*)(Args...);
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TypeFactory() = default;
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/**
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* @brief Registers a Derived type under the given id.
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*
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* Requirements (checked at compile-time):
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* - Derived must inherit from BaseClass
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* - Derived must be constructible from Args...
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*
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* Re-registering the same id overwrites the previous entry ("last wins").
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*/
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template <class Derived>
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void registerType(const ClassId& id) {
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static_assert(std::is_base_of_v<BaseClass, Derived>,
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"Derived must inherit from BaseClass");
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static_assert(std::is_constructible_v<Derived, Args...>,
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"Derived must be constructible from Args...");
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classes.insert_or_assign(id, &instantiate<Derived>);
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}
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/**
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* @brief Returns creator function for the given id.
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* @throws std::out_of_range when id is not registered.
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*/
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[[nodiscard]] CreatorFn creator(const ClassId& id) const {
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return classes.at(id);
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}
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/**
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* @brief Creates an instance for the given id using provided arguments.
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* @throws std::out_of_range when id is not registered.
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*/
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[[nodiscard]] BasePtr create(const ClassId& id, Args... args) const {
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return creator(id)(std::move(args)...);
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}
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/**
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* @brief Checks whether an id is registered.
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*/
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[[nodiscard]] bool contains(const ClassId& id) const {
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return classes.find(id) != classes.end();
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}
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protected:
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// Protected by design: derived factories may extend/inspect the registry.
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std::unordered_map<ClassId, CreatorFn> classes;
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private:
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template <class Derived>
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static BasePtr instantiate(Args... args) {
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return std::make_shared<Derived>(std::move(args)...);
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}
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};
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#endif // TYPEFACTORY_H
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