defer in C++

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defer allows the program to automatically release a source on demand. It is a Go keyword, but can be implemented in C++ with std::unique_ptr:

#include <functional>
template<typename T> using deleted_unique_ptr = std::unique_ptr<T, std::function<void(T*)>>;

And use it like

{
    deleted_unique_ptr<T> dptr(
        raw_ptr,
        [](auto p) { delete_func(p); }
    );
}

The C++ world prefer to call this RAII scope guard, the resource release function is called automatically when the std::unique_ptr object is deconstructed, i.e. on leaving the scope.

However, you can take one more step and make it imperative just like in Go.

#include <functional>
#define CONCAT(a, b) a ## b
#define __defer_impl(ptr, dfn, l)                               \
    std::unique_ptr<std::remove_pointer<decltype(ptr)>::type,   \
                    std::function<void(decltype(ptr))>>         \
    CONCAT(__dtor, l) (ptr, [](decltype(ptr) p) { dfn(p); })
#define defer(ptr, dfn) __defer_impl(ptr, dfn, __COUNTER__) // __LINE__ works as well

The CONCAT() macro is there to make sure __COUNTER__ expands, otherwise concatenate operator ## will suppress it.

Also, a std::experimental::unique_resource is around the corner.