Simple defer macro for c++

defer.cpp

// SPDX-FileCopyrightText: 2015 Marek Rusinowski
// SPDX-License-Identifier: MIT
#include <memory>
#include <cstdio>

template<typename F>
class defer_finalizer {
    F f;
    bool moved;
  public:
    template<typename T>
    defer_finalizer(T && f_) : f(std::forward<T>(f_)), moved(false) { }

    defer_finalizer(const defer_finalizer &) = delete;

    defer_finalizer(defer_finalizer && other) : f(std::move(other.f)), moved(other.moved) {
        other.moved = true;
    }

    ~defer_finalizer() {
        if (!moved) f();
    }
};

struct {
    template<typename F>
    defer_finalizer<F> operator<<(F && f) {
        return defer_finalizer<F>(std::forward<F>(f));
    }
} deferrer;

#define TOKENPASTE(x, y) x ## y
#define TOKENPASTE2(x, y) TOKENPASTE(x, y)
#define defer auto TOKENPASTE2(__deferred_lambda_call, __COUNTER__) = deferrer << [&]

void f() {
    FILE *f = fopen("asdasd", "r");
    defer {
        fclose(f);
    };
}

// Compiler optimizes it nicely: http://goo.gl/XAGl6A

Hi! I really like this but I'm never sure if I can use it officially. Would you mind providing a license for this code?

@paulfd Sure, I've added the license header, it's MIT.

Thanks alot :)

How can I make this a header file, maybe change deferrer to a static singleton instance?

@dolmens I know about 2 ways:

1. Add static to the deferrer singleton as you suggest.

2. struct deferrer {
        // ...
   };
   extern deferrer deferrer_object;

   and then have a single c++ file with deferrer deferrer_object;

The 1 is cleaner IMHO ;)