C++11 defer scope implementation

defer.h

// defer.h
//
// Copyright (c) 2016 Victor Moneratto
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this software
// and associated documentation files (the "Software"), to deal in the Software without restriction,
// including without limitation the rights to use, copy, modify, merge, publish, distribute,
// sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or substantial
// portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
// NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

#pragma once

template <typename Func>
struct ScopeExit {
	Func f;
	ScopeExit(const Func& f) : f(f) {}
	~ScopeExit() { f(); }
};

struct ScopeExitHelper {
	template <typename Func>
	ScopeExit<Func> operator+(Func func) { return func; }
};

#define CONCAT_INTERNAL(x,y) x##y
#define CONCAT(x,y) CONCAT_INTERNAL(x,y)

#define defer const auto& CONCAT(scope_exit_, __LINE__) = ScopeExitHelper() + [&]()

// Usage:
// int* mem = (int*) malloc(sizeof(int) * 1024);
// defer { free(mem); };