tdesktop/Telegram/SourceFiles/base/lambda.h

/*
This file is part of Telegram Desktop,
the official desktop application for the Telegram messaging service.

For license and copyright information please follow this link:
https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
*/
#pragma once

#include <memory>

#ifndef CUSTOM_LAMBDA_WRAP

#include <functional>
#include "base/unique_function.h"

namespace base {

template <typename Function>
using lambda = std::function<Function>;

template <typename Function>
using lambda_once = unique_function<Function>;

namespace lambda_internal {

template <typename Lambda>
struct lambda_call_type {
	using type = decltype(&Lambda::operator());
};

} // namespace lambda_internal

template <typename Lambda>
using lambda_call_type_t
	= typename lambda_internal::lambda_call_type<Lambda>::type;

} // namespace base

#else // CUSTOM_LAMBDA_WRAP

#ifndef Assert
#define LambdaAssertDefined
#define Assert(v) ((v) ? ((void)0) : std::abort())
#endif // Assert

#ifndef Unexpected
#define LambdaUnexpectedDefined
#define Unexpected(v) std::abort()
#endif // Unexpected

namespace base {

template <typename Function> class lambda_once;
template <typename Function> class lambda;

// Get lambda type from a lambda template parameter.

namespace lambda_internal {

template <typename FunctionType>
struct type_resolver;

template <typename Lambda, typename R, typename ...Args>
struct type_resolver<R(Lambda::*)(Args...) const> {
	using type = lambda<R(Args...)>;
	static constexpr auto is_mutable = false;
};

template <typename Lambda, typename R, typename ...Args>
struct type_resolver<R(Lambda::*)(Args...)> {
	using type = lambda_once<R(Args...)>;
	static constexpr auto is_mutable = true;
};

template <typename Lambda>
struct type_helper {
	using type = typename type_resolver<decltype(&Lambda::operator())>::type;
	static constexpr auto is_mutable = type_resolver<decltype(&Lambda::operator())>::is_mutable;
};

} // namespace lambda_internal

template <typename Lambda>
using lambda_type = typename lambda_internal::type_helper<std::decay_t<Lambda>>::type;

namespace lambda_internal {

constexpr auto kFullStorageSize = 32U;
static_assert(kFullStorageSize % sizeof(void*) == 0, "Invalid pointer size!");

constexpr auto kStorageSize = kFullStorageSize - sizeof(void*);
using alignment = std::max_align_t;

template <typename Lambda>
constexpr bool is_large = (sizeof(std::decay_t<Lambda>) > kStorageSize);

[[noreturn]] inline void bad_construct_copy(void *lambda, const void *source) {
	Unexpected("base::lambda bad_construct_copy() called!");
}

template <typename Return, typename ...Args>
[[noreturn]] Return bad_const_call(const void *lambda, Args...) {
	Unexpected("base::lambda bad_const_call() called!");
}

template <typename Return, typename ...Args>
struct vtable_base {
	using construct_copy_other_type = void(*)(void *, const void *); // dst, src
	using construct_move_other_type = void(*)(void *, void *); // dst, src
	using const_call_type = Return(*)(const void *, Args...);
	using call_type = Return(*)(void *, Args...);
	using destruct_type = void(*)(const void *);

	vtable_base() = delete;
	vtable_base(const vtable_base &other) = delete;
	vtable_base &operator=(const vtable_base &other) = delete;

	vtable_base(
		construct_copy_other_type construct_copy_other,
		construct_move_other_type construct_move_other,
		const_call_type const_call,
		call_type call,
		destruct_type destruct)
		: construct_copy_other(construct_copy_other)
		, construct_move_other(construct_move_other)
		, const_call(const_call)
		, call(call)
		, destruct(destruct) {
	}

	const construct_copy_other_type construct_copy_other;
	const construct_move_other_type construct_move_other;
	const const_call_type const_call;
	const call_type call;
	const destruct_type destruct;

};

template <typename Lambda, bool IsLarge, typename Return, typename ...Args> struct vtable_once_impl;

template <typename Lambda, typename Return, typename ...Args>
struct vtable_once_impl<Lambda, true, Return, Args...> : public vtable_base<Return, Args...> {
	using JustLambda = std::decay_t<Lambda>;
	using LambdaPtr = std::unique_ptr<JustLambda>;
	using Parent = vtable_base<Return, Args...>;
	static void construct_move_other_method(void *storage, void *source) {
		auto source_lambda_ptr = static_cast<LambdaPtr*>(source);
		new (storage) LambdaPtr(std::move(*source_lambda_ptr));
	}
	static Return call_method(void *storage, Args... args) {
		return (**static_cast<LambdaPtr*>(storage))(std::forward<Args>(args)...);
	}
	static void destruct_method(const void *storage) {
		static_cast<const LambdaPtr*>(storage)->~LambdaPtr();
	}
	vtable_once_impl() : Parent(
		&bad_construct_copy,
		&vtable_once_impl::construct_move_other_method,
		&bad_const_call<Return, Args...>,
		&vtable_once_impl::call_method,
		&vtable_once_impl::destruct_method) {
	}

	// Used directly.
	static void construct_move_lambda_method(void *storage, void *source) {
		auto source_lambda = static_cast<JustLambda*>(source);
		new (storage) LambdaPtr(std::make_unique<JustLambda>(static_cast<JustLambda&&>(*source_lambda)));
	}

protected:
	vtable_once_impl(
		typename Parent::construct_copy_other_type construct_copy_other,
		typename Parent::const_call_type const_call
	) : Parent(
		construct_copy_other,
		&vtable_once_impl::construct_move_other_method,
		const_call,
		&vtable_once_impl::call_method,
		&vtable_once_impl::destruct_method) {
	}

};

template <typename Lambda, typename Return, typename ...Args>
struct vtable_once_impl<Lambda, false, Return, Args...> : public vtable_base<Return, Args...> {
	using JustLambda = std::decay_t<Lambda>;
	using Parent = vtable_base<Return, Args...>;
	static void construct_move_other_method(void *storage, void *source) {
		auto source_lambda = static_cast<JustLambda*>(source);
		new (storage) JustLambda(static_cast<JustLambda&&>(*source_lambda));
	}
	static Return call_method(void *storage, Args... args) {
		return (*static_cast<JustLambda*>(storage))(std::forward<Args>(args)...);
	}
	static void destruct_method(const void *storage) {
		static_cast<const JustLambda*>(storage)->~JustLambda();
	}
	vtable_once_impl() : Parent(
		&bad_construct_copy,
		&vtable_once_impl::construct_move_other_method,
		&bad_const_call<Return, Args...>,
		&vtable_once_impl::call_method,
		&vtable_once_impl::destruct_method) {
	}

	// Used directly.
	static void construct_move_lambda_method(void *storage, void *source) {
		auto source_lambda = static_cast<JustLambda*>(source);
		new (storage) JustLambda(static_cast<JustLambda&&>(*source_lambda));
	}

protected:
	vtable_once_impl(
		typename Parent::construct_copy_other_type construct_copy_other,
		typename Parent::const_call_type const_call
	) : Parent(
		construct_copy_other,
		&vtable_once_impl::construct_move_other_method,
		const_call,
		&vtable_once_impl::call_method,
		&vtable_once_impl::destruct_method) {
	}

};

template <typename Lambda, typename Return, typename ...Args>
struct vtable_once : public vtable_once_impl<Lambda, is_large<Lambda>, Return, Args...> {
	static const vtable_once instance;
};

template <typename Lambda, typename Return, typename ...Args>
const vtable_once<Lambda, Return, Args...> vtable_once<Lambda, Return, Args...>::instance = {};

template <typename Lambda, bool IsLarge, typename Return, typename ...Args> struct vtable_impl;

template <typename Lambda, typename Return, typename ...Args>
struct vtable_impl<Lambda, true, Return, Args...> : public vtable_once_impl<Lambda, true, Return, Args...> {
	using JustLambda = std::decay_t<Lambda>;
	using LambdaPtr = std::unique_ptr<JustLambda>;
	using Parent = vtable_once_impl<Lambda, true, Return, Args...>;
	static void construct_copy_other_method(void *storage, const void *source) {
		auto source_lambda = static_cast<const LambdaPtr*>(source);
		new (storage) LambdaPtr(std::make_unique<JustLambda>(*source_lambda->get()));
	}
	static Return const_call_method(const void *storage, Args... args) {
		auto lambda_ptr = static_cast<const LambdaPtr*>(storage)->get();
		return (*static_cast<const JustLambda*>(lambda_ptr))(std::forward<Args>(args)...);
	}
	vtable_impl() : Parent(
		&vtable_impl::construct_copy_other_method,
		&vtable_impl::const_call_method
	) {
	}

};

template <typename Lambda, typename Return, typename ...Args>
struct vtable_impl<Lambda, false, Return, Args...> : public vtable_once_impl<Lambda, false, Return, Args...> {
	using JustLambda = std::decay_t<Lambda>;
	using Parent = vtable_once_impl<Lambda, false, Return, Args...>;
	static void construct_copy_other_method(void *storage, const void *source) {
		auto source_lambda = static_cast<const JustLambda*>(source);
		new (storage) JustLambda(static_cast<const JustLambda &>(*source_lambda));
	}
	static Return const_call_method(const void *storage, Args... args) {
		return (*static_cast<const JustLambda*>(storage))(std::forward<Args>(args)...);
	}
	vtable_impl() : Parent(
		&vtable_impl::construct_copy_other_method,
		&vtable_impl::const_call_method
	) {
	}

};

template <typename Lambda, typename Return, typename ...Args>
struct vtable : public vtable_impl<Lambda, is_large<Lambda>, Return, Args...> {
	static const vtable instance;
};

template <typename Lambda, typename Return, typename ...Args>
const vtable<Lambda, Return, Args...> vtable<Lambda, Return, Args...>::instance = {};

} // namespace lambda_internal

template <typename Return, typename ...Args>
class lambda_once<Return(Args...)> {
	using VTable = lambda_internal::vtable_base<Return, Args...>;

public:
	using return_type = Return;

	lambda_once() {
		data_.vtable = nullptr;
	}
	lambda_once(const lambda_once &other) = delete;
	lambda_once &operator=(const lambda_once &other) = delete;

	// Move construct / assign from the same type.
	lambda_once(lambda_once &&other) {
		if ((data_.vtable = other.data_.vtable)) {
			data_.vtable->construct_move_other(data_.storage, other.data_.storage);
		}
	}
	lambda_once &operator=(lambda_once &&other) {
		if (this != &other) {
			if (data_.vtable) {
				data_.vtable->destruct(data_.storage);
			}
			if ((data_.vtable = other.data_.vtable)) {
				data_.vtable->construct_move_other(data_.storage, other.data_.storage);
				data_.vtable->destruct(other.data_.storage);
				other.data_.vtable = nullptr;
			}
		}
		return *this;
	}

	// Move construct / assign from a derived type.
	lambda_once(lambda<Return(Args...)> &&other) {
		if ((data_.vtable = other.data_.vtable)) {
			data_.vtable->construct_move_other(data_.storage, other.data_.storage);
			data_.vtable->destruct(other.data_.storage);
			other.data_.vtable = nullptr;
		}
	}
	lambda_once &operator=(lambda<Return(Args...)> &&other) {
		if (this != &other) {
			if (data_.vtable) {
				data_.vtable->destruct(data_.storage);
			}
			if ((data_.vtable = other.data_.vtable)) {
				data_.vtable->construct_move_other(data_.storage, other.data_.storage);
				data_.vtable->destruct(other.data_.storage);
				other.data_.vtable = nullptr;
			}
		}
		return *this;
	}

	// Copy construct / assign from a derived type.
	lambda_once(const lambda<Return(Args...)> &other) {
		if ((data_.vtable = other.data_.vtable)) {
			data_.vtable->construct_copy_other(data_.storage, other.data_.storage);
		}
	}
	lambda_once &operator=(const lambda<Return(Args...)> &other) {
		if (this != &other) {
			if (data_.vtable) {
				data_.vtable->destruct(data_.storage);
			}
			if ((data_.vtable = other.data_.vtable)) {
				data_.vtable->construct_copy_other(data_.storage, other.data_.storage);
			}
		}
		return *this;
	}

	// Copy / move construct / assign from an arbitrary type.
	template <typename Lambda, typename = std::enable_if_t<std::is_convertible<decltype(std::declval<Lambda>()(std::declval<Args>()...)),Return>::value>>
	lambda_once(Lambda other) {
		data_.vtable = &lambda_internal::vtable_once<Lambda, Return, Args...>::instance;
		lambda_internal::vtable_once<Lambda, Return, Args...>::construct_move_lambda_method(data_.storage, &other);
	}
	template <typename Lambda, typename = std::enable_if_t<std::is_convertible<decltype(std::declval<Lambda>()(std::declval<Args>()...)),Return>::value>>
	lambda_once &operator=(Lambda other) {
		if (data_.vtable) {
			data_.vtable->destruct(data_.storage);
		}
		data_.vtable = &lambda_internal::vtable_once<Lambda, Return, Args...>::instance;
		lambda_internal::vtable_once<Lambda, Return, Args...>::construct_move_lambda_method(data_.storage, &other);
		return *this;
	}

	void swap(lambda_once &other) {
		if (this != &other) {
			std::swap(*this, other);
		}
	}

	template <
		typename ...OtherArgs,
		typename = std::enable_if_t<(sizeof...(Args) == sizeof...(OtherArgs))>>
	inline Return operator()(OtherArgs&&... args) {
		Assert(data_.vtable != nullptr);
		return data_.vtable->call(
			data_.storage,
			std::forward<OtherArgs>(args)...);
	}

	explicit operator bool() const {
		return (data_.vtable != nullptr);
	}

	~lambda_once() {
		if (data_.vtable) {
			data_.vtable->destruct(data_.storage);
		}
	}

protected:
	struct Private {
	};
	lambda_once(const VTable *vtable, const Private &) {
		data_.vtable = vtable;
	}

	struct Data {
		char storage[lambda_internal::kStorageSize];
		const VTable *vtable;
	};
	union {
		lambda_internal::alignment alignment_;
		char raw_[lambda_internal::kFullStorageSize];
		Data data_;
	};

};

template <typename Return, typename ...Args>
class lambda<Return(Args...)> final : public lambda_once<Return(Args...)> {
	using Parent = lambda_once<Return(Args...)>;

public:
	lambda() = default;

	// Move construct / assign from the same type.
	lambda(lambda<Return(Args...)> &&other) : Parent(std::move(other)) {
	}
	lambda &operator=(lambda<Return(Args...)> &&other) {
		Parent::operator=(std::move(other));
		return *this;
	}

	// Copy construct / assign from the same type.
	lambda(const lambda<Return(Args...)> &other) : Parent(other) {
	}
	lambda &operator=(const lambda<Return(Args...)> &other) {
		Parent::operator=(other);
		return *this;
	}

	// Copy / move construct / assign from an arbitrary type.
	template <typename Lambda, typename = std::enable_if_t<std::is_convertible<decltype(std::declval<Lambda>()(std::declval<Args>()...)),Return>::value>>
	lambda(Lambda other) : Parent(&lambda_internal::vtable<Lambda, Return, Args...>::instance, typename Parent::Private()) {
		lambda_internal::vtable<Lambda, Return, Args...>::construct_move_lambda_method(this->data_.storage, &other);
	}
	template <typename Lambda, typename = std::enable_if_t<std::is_convertible<decltype(std::declval<Lambda>()(std::declval<Args>()...)),Return>::value>>
	lambda &operator=(Lambda other) {
		if (this->data_.vtable) {
			this->data_.vtable->destruct(this->data_.storage);
		}
		this->data_.vtable = &lambda_internal::vtable<Lambda, Return, Args...>::instance;
		lambda_internal::vtable<Lambda, Return, Args...>::construct_move_lambda_method(this->data_.storage, &other);
		return *this;
	}

	template <
		typename ...OtherArgs,
		typename = std::enable_if_t<(sizeof...(Args) == sizeof...(OtherArgs))>>
	inline Return operator()(OtherArgs&&... args) const {
		Assert(this->data_.vtable != nullptr);
		return this->data_.vtable->const_call(
			this->data_.storage,
			std::forward<OtherArgs>(args)...);
	}

	void swap(lambda &other) {
		if (this != &other) {
			std::swap(*this, other);
		}
	}

};

} // namespace base

#ifdef LambdaAssertDefined
#undef Assert
#endif // LambdaAssertDefined

#ifdef LambdaUnexpectedDefined
#undef Unexpected
#endif // LambdaUnexpectedDefined

#endif // CUSTOM_LAMBDA_WRAP