Add a simple signal implementation to util

libs/util/include/psemek/util/signal.hpp

@@ -0,0 +1,79 @@
+#pragma once
+
+#include <psemek/util/function.hpp>
+
+#include <list>
+#include <memory>
+
+namespace psemek::util
+{
+
+	template <typename T>
+	struct signal
+	{
+		using subscriber = function<void(T const &)>;
+		using subscription_token = std::shared_ptr<void>;
+
+		[[nodiscard]] subscription_token subscribe(subscriber callback) const
+		{
+			auto token = std::make_shared<subscriber>(std::move(callback));
+			subscribers_.push_back(std::weak_ptr{token});
+			return token;
+		}
+
+		void operator()(T const & value)
+		{
+			auto begin = subscribers_.begin();
+			auto end = subscribers_.end();
+
+			for (auto it = begin; it != end;)
+			{
+				if (auto callback = it->lock())
+				{
+					(*callback)(value);
+					++it;
+				}
+				else
+					it = subscribers_.erase(it);
+			}
+		}
+
+	private:
+		mutable std::list<std::weak_ptr<subscriber>> subscribers_;
+	};
+
+	template <>
+	struct signal<void>
+	{
+		using subscriber = function<void()>;
+		using subscribtion_token = std::shared_ptr<void>;
+
+		[[nodiscard]] subscribtion_token subscribe(subscriber callback) const
+		{
+			auto token = std::make_shared<subscriber>(std::move(callback));
+			subscribers_.push_back(std::weak_ptr{token});
+			return token;
+		}
+
+		void operator()()
+		{
+			auto begin = subscribers_.begin();
+			auto end = subscribers_.end();
+
+			for (auto it = begin; it != end;)
+			{
+				if (auto callback = it->lock())
+				{
+					(*callback)();
+					++it;
+				}
+				else
+					it = subscribers_.erase(it);
+			}
+		}
+
+	private:
+		mutable std::list<std::weak_ptr<subscriber>> subscribers_;
+	};
+
+}