From a1cf64663387a7cdb1c174bf6c87d0918f5d0c07 Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Sun, 22 Nov 2020 12:06:55 +0300
Subject: [PATCH] Rename movable_function -> function & better SSO

---
 libs/async/include/psemek/async/executor.hpp  |   4 +-
 .../async/include/psemek/async/threadpool.hpp |   2 -
 libs/util/include/psemek/util/function.hpp    | 166 ++++++++++++++++++
 .../include/psemek/util/movable_function.hpp  |  89 ----------
 .../{movable_function.cpp => function.cpp}    |   2 +-
 5 files changed, 169 insertions(+), 94 deletions(-)
 create mode 100644 libs/util/include/psemek/util/function.hpp
 delete mode 100644 libs/util/include/psemek/util/movable_function.hpp
 rename libs/util/source/{movable_function.cpp => function.cpp} (77%)

diff --git a/libs/async/include/psemek/async/executor.hpp b/libs/async/include/psemek/async/executor.hpp
index dbce58d8..01167acd 100644
--- a/libs/async/include/psemek/async/executor.hpp
+++ b/libs/async/include/psemek/async/executor.hpp
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <psemek/util/movable_function.hpp>
+#include <psemek/util/function.hpp>
 
 #include <future>
 #include <chrono>
@@ -135,7 +135,7 @@ namespace psemek::async
 
 	struct executor
 	{
-		using task = util::movable_function<void()>;
+		using task = util::function<void()>;
 		using clock = std::chrono::high_resolution_clock;
 
 		// Post the task for execution. Where and when will
diff --git a/libs/async/include/psemek/async/threadpool.hpp b/libs/async/include/psemek/async/threadpool.hpp
index aa8211da..23419c81 100644
--- a/libs/async/include/psemek/async/threadpool.hpp
+++ b/libs/async/include/psemek/async/threadpool.hpp
@@ -1,10 +1,8 @@
 #pragma once
 
 #include <psemek/async/executor.hpp>
-
 #include <psemek/util/thread.hpp>
 #include <psemek/util/synchronyzed_queue.hpp>
-#include <psemek/util/movable_function.hpp>
 
 #include <future>
 #include <vector>
diff --git a/libs/util/include/psemek/util/function.hpp b/libs/util/include/psemek/util/function.hpp
new file mode 100644
index 00000000..666f0539
--- /dev/null
+++ b/libs/util/include/psemek/util/function.hpp
@@ -0,0 +1,166 @@
+#pragma once
+
+#include <type_traits>
+#include <memory>
+
+namespace psemek::util
+{
+
+	namespace detail
+	{
+
+		// Implemented in cpp to prevent dependency on <functional>
+		[[noreturn]] void bad_function_call();
+
+	}
+
+	template <typename Signature>
+	struct function;
+
+	template <typename R, typename ... Args>
+	struct function<R(Args...)>
+	{
+		using signature = R(Args...);
+
+		function() noexcept = default;
+
+		template <typename F>
+		function(F && f);
+
+		function (function &&) noexcept;
+		function & operator = (function &&) noexcept;
+
+		function (function const &) = delete;
+		function & operator = (function const &) = delete;
+
+		template <typename F>
+		function & operator = (F && f);
+
+		explicit operator bool() const
+		{
+			return static_cast<bool>(vtable_);
+		}
+
+		template <typename ... Args1>
+		R operator()(Args1 && ... args) const;
+
+		void reset();
+
+	private:
+		static constexpr std::size_t storage_size = sizeof(void*) * 3;
+		static constexpr std::size_t storage_align = alignof(void*);
+
+		std::aligned_storage_t<storage_size, storage_align> storage_;
+
+		struct vtable
+		{
+			using move_func = void(*)(void *, void *);
+			using destroy_func = void(*)(void *);
+			using call_func = R(*)(void *, Args ...);
+
+			move_func move;
+			destroy_func destroy;
+			call_func call;
+		};
+
+		vtable * vtable_ = nullptr;
+
+		template <typename F>
+		void assign(F && f);
+	};
+
+	template <typename R, typename ... Args>
+	template <typename F>
+	function<R(Args...)>::function(F && f)
+	{
+		assign(std::forward<F>(f));
+	}
+
+	template <typename R, typename ... Args>
+	template <typename F>
+	function<R(Args...)> & function<R(Args...)>::operator = (F && f)
+	{
+		reset();
+		assign(std::forward<F>(f));
+		return *this;
+	}
+
+	template <typename R, typename ... Args>
+	function<R(Args...)>::function (function && other) noexcept
+	{
+		vtable_ = other.vtable_;
+		vtable_->move(&other.storage_, &storage_);
+		other.reset();
+	}
+
+	template <typename R, typename ... Args>
+	function<R(Args...)> & function<R(Args...)>::operator = (function && other) noexcept
+	{
+		if (this == &other)
+			return *this;
+
+		vtable_ = other.vtable_;
+		vtable_->move(&other.storage_, &storage_);
+		other.reset();
+		return *this;
+	}
+
+	template <typename R, typename ... Args>
+	template <typename ... Args1>
+	R function<R(Args...)>::operator()(Args1 && ... args) const
+	{
+		if (!vtable_)
+			detail::bad_function_call();
+
+		return vtable_->call(const_cast<void *>(static_cast<void const *>(&storage_)), std::forward<Args1>(args)...);
+	}
+
+	template <typename R, typename ... Args>
+	void function<R(Args...)>::reset()
+	{
+		if (!vtable_) return;
+
+		vtable_->destroy(&storage_);
+		vtable_ = nullptr;
+	}
+
+	template <typename R, typename ... Args>
+	template <typename F>
+	void function<R(Args...)>::assign(F && f)
+	{
+		using T = std::decay_t<F>;
+
+		constexpr bool static_storage = true
+			&& sizeof(T) <= storage_size
+			&& alignof(T) <= storage_align
+			&& ((storage_align % alignof(T)) == 0)
+			&& std::is_nothrow_move_constructible_v<T>
+			;
+
+		if constexpr (static_storage)
+		{
+			new (reinterpret_cast<T *>(&storage_)) T(std::move(f));
+
+			static vtable m = {
+				[](void * src, void * dst){ new (reinterpret_cast<T*>(dst)) T(std::move(*reinterpret_cast<T*>(src))); },
+				[](void * src){ reinterpret_cast<T*>(src)->~T(); },
+				[](void * src, Args ... args) -> R { return (*reinterpret_cast<T*>(src))(static_cast<Args&&>(args)...); }
+			};
+
+			vtable_ = &m;
+		}
+		else
+		{
+			*reinterpret_cast<T**>(&storage_) = new T(std::move(f));
+
+			static vtable m = {
+				[](void * src, void * dst){ *reinterpret_cast<T**>(dst) = *reinterpret_cast<T**>(src); *reinterpret_cast<T**>(src) = nullptr; },
+				[](void * src){ delete *reinterpret_cast<T**>(src); },
+				[](void * src, Args ... args) -> R { return (**reinterpret_cast<T**>(src))(static_cast<Args&&>(args)...); }
+			};
+
+			vtable_ = &m;
+		}
+	}
+
+}
diff --git a/libs/util/include/psemek/util/movable_function.hpp b/libs/util/include/psemek/util/movable_function.hpp
deleted file mode 100644
index 6bdc4a5c..00000000
--- a/libs/util/include/psemek/util/movable_function.hpp
+++ /dev/null
@@ -1,89 +0,0 @@
-#pragma once
-
-#include <psemek/util/polymorphic_storage.hpp>
-
-#include <memory>
-
-namespace psemek::util
-{
-
-	namespace detail
-	{
-
-		template <typename Signature>
-		struct movable_function_node_base;
-
-		template <typename R, typename ... Args>
-		struct movable_function_node_base<R(Args...)>
-		{
-			virtual R call(Args ...) = 0;
-
-			virtual ~movable_function_node_base() = default;
-		};
-
-		template <typename Signature, typename F>
-		struct movable_function_node;
-
-		template <typename R, typename ... Args, typename F>
-		struct movable_function_node<R(Args...), F>
-			: movable_function_node_base<R(Args...)>
-		{
-			F f;
-
-			movable_function_node(F && f)
-				: f(std::move(f))
-			{}
-
-			R call(Args ... args) override
-			{
-				return f(args...);
-			}
-		};
-
-		// Implemented in cpp to prevent dependency on <functional>
-		[[noreturn]] void bad_function_call();
-
-	}
-
-	template <typename Signature>
-	struct movable_function;
-
-	template <typename R, typename ... Args>
-	struct movable_function<R(Args...)>
-	{
-		using signature = R(Args...);
-
-		movable_function() noexcept = default;
-
-		template <typename F>
-		movable_function(F f)
-		{
-			storage_.template emplace<detail::movable_function_node<signature, std::decay_t<F>>>(std::move(f));
-		}
-
-		movable_function (movable_function &&) noexcept = default;
-		movable_function & operator = (movable_function &&) noexcept = default;
-
-		movable_function (movable_function const &) = delete;
-		movable_function & operator = (movable_function const &) = delete;
-
-		explicit operator bool() const
-		{
-			return static_cast<bool>(storage_);
-		}
-
-		template <typename ... Args1>
-		R operator()(Args1 && ... args) const
-		{
-			if (!storage_)
-				detail::bad_function_call();
-
-			return storage_.get()->call(std::forward<Args1>(args)...);
-		}
-
-	private:
-		static constexpr std::size_t small_storage_size = sizeof(void*) * 3;
-		polymorhpic_storage<detail::movable_function_node_base<signature>, small_storage_size> storage_;
-	};
-
-}
diff --git a/libs/util/source/movable_function.cpp b/libs/util/source/function.cpp
similarity index 77%
rename from libs/util/source/movable_function.cpp
rename to libs/util/source/function.cpp
index 26fb51e5..b2c513fb 100644
--- a/libs/util/source/movable_function.cpp
+++ b/libs/util/source/function.cpp
@@ -1,4 +1,4 @@
-#include <psemek/util/movable_function.hpp>
+#include <psemek/util/function.hpp>
 
 #include <functional>