Proposal for observers and deferred implementations (#1599)

dCommon/Implementation.h

@@ -0,0 +1,92 @@
+#ifndef __IMPLEMENTATION_H__
+#define __IMPLEMENTATION_H__
+
+#include <functional>
+#include <optional>
+
+/**
+ * @brief A way to defer the implementation of an action.
+ * 
+ * @tparam R The result of the action.
+ * @tparam T The types of the arguments that the implementation requires.
+ */
+template <typename R, typename... T>
+class Implementation {
+public:
+	typedef std::function<std::optional<R>(T...)> ImplementationFunction;
+
+	/**
+	 * @brief Sets the implementation of the action.
+	 * 
+	 * @param implementation The implementation of the action.
+	 */
+	void SetImplementation(const ImplementationFunction& implementation) {
+		this->implementation = implementation;
+	}
+
+	/**
+	 * @brief Clears the implementation of the action.
+	 */
+	void ClearImplementation() {
+		implementation.reset();
+	}
+
+	/**
+	 * @brief Checks if the implementation is set.
+	 * 
+	 * @return true If the implementation is set.
+	 * @return false If the implementation is not set.
+	 */
+	bool IsSet() const {
+		return implementation.has_value();
+	}
+
+	/**
+	 * @brief Executes the implementation if it is set.
+	 * 
+	 * @param args The arguments to pass to the implementation.
+	 * @return std::optional<R> The optional result of the implementation. If the result is not set, it indicates that the default action should be taken.
+	 */
+	std::optional<R> Execute(T... args) const {
+		return IsSet() ? implementation.value()(args...) : std::nullopt;
+	}
+
+	/**
+	 * @brief Exectues the implementation if it is set, otherwise returns a default value.
+	 * 
+	 * @param args The arguments to pass to the implementation.
+	 * @param defaultValue The default value to return if the implementation is not set or should not be deferred.
+	 */
+	R ExecuteWithDefault(T... args, const R& defaultValue) const {
+		return Execute(args...).value_or(defaultValue);
+	}
+
+	/**
+	 * = operator overload.
+	 */
+	Implementation& operator=(const Implementation& other) {
+		implementation = other.implementation;
+		return *this;
+	}
+
+	/**
+	 * = operator overload.
+	 */
+	Implementation& operator=(const ImplementationFunction& implementation) {
+		this->implementation = implementation;
+		return *this;
+	}
+
+	/**
+	 * () operator overload.
+	 */
+	std::optional<R> operator()(T... args) {
+		return !IsSet() ? std::nullopt : implementation(args...);
+	}
+
+private:
+	std::optional<ImplementationFunction> implementation;
+
+};
+
+#endif  //!__IMPLEMENTATION_H__

dCommon/Observable.h

@@ -0,0 +1,73 @@
+#ifndef __OBSERVABLE_H__
+#define __OBSERVABLE_H__
+
+#include <vector>
+#include <functional>
+
+/**
+ * @brief An event which can be observed by multiple observers.
+ * 
+ * @tparam T The types of the arguments to be passed to the observers.
+ */
+template <typename... T>
+class Observable {
+public:
+	typedef std::function<void(T...)> Observer;
+
+	/**
+	 * @brief Adds an observer to the event.
+	 * 
+	 * @param observer The observer to add.
+	 */
+	void AddObserver(const Observer& observer) {
+		observers.push_back(observer);
+	}
+
+	/**
+	 * @brief Removes an observer from the event.
+	 * 
+	 * @param observer The observer to remove.
+	 */
+	void RemoveObserver(const Observer& observer) {
+		observers.erase(std::remove(observers.begin(), observers.end(), observer), observers.end());
+	}
+
+	/**
+	 * @brief Notifies all observers of the event.
+	 * 
+	 * @param args The arguments to pass to the observers.
+	 */
+	void Notify(T... args) {
+		for (const auto& observer : observers) {
+			observer(args...);
+		}
+	}
+
+	/**
+	 * += operator overload.
+	 */
+	Observable& operator+=(const Observer& observer) {
+		AddObserver(observer);
+		return *this;
+	}
+
+	/**
+	 * -= operator overload.
+	 */
+	Observable& operator-=(const Observer& observer) {
+		RemoveObserver(observer);
+		return *this;
+	}
+	
+	/**
+	 * () operator overload.
+	 */
+	void operator()(T... args) {
+		Notify(args...);
+	}
+
+private:
+	std::vector<Observer> observers;
+};
+
+#endif  //!__OBSERVABLE_H__