tdesktop/Telegram/SourceFiles/base/functors.h

/*
This file is part of Telegram Desktop,
the official desktop version of Telegram messaging app, see https://telegram.org

Telegram Desktop is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

It is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

In addition, as a special exception, the copyright holders give permission
to link the code of portions of this program with the OpenSSL library.

Full license: https://github.com/telegramdesktop/tdesktop/blob/master/LICENSE
Copyright (c) 2014-2017 John Preston, https://desktop.telegram.org
*/
#pragma once

namespace base {
namespace functors {

struct abs_helper {
	template <
		typename Type,
		typename = decltype(0 < std::declval<Type>()),
		typename = decltype(-std::declval<Type>())>
	constexpr Type operator()(Type value) const {
		return (0 < value) ? value : (-value);
	}
};
constexpr auto abs = abs_helper{};

constexpr auto add = [](auto value) {
	return [value](auto other) {
		return value + other;
	};
};

struct negate_helper {
	template <
		typename Type,
		typename = decltype(-std::declval<Type>())>
	constexpr Type operator()(Type value) const {
		return -value;
	}
};
constexpr auto negate = negate_helper{};

} // namespace functors
} // namespace base