krzaq / resource

Universal resource handling class template for C++

This is the unviersal class resource class. All init, cleanup routines can be expressed as policies, with good defaults already provided. Policies can also be used to choose storage and copy behaviour.

unique_ptr-like behaviour

using Res = resource<int>;
Res ptr1{new int{42}};
Res ptr2; // ptr2{nullptr}

// ptr2 = ptr1; // error
ptr2 = std::move(ptr1); // ok

// ptr2 gets deleted at the end of scope

with an array

using Res = resource<int[]>;
Res ptr1{new int[42]};
Res ptr2; // ptr2{nullptr}

// ptr2 = ptr1; // error
ptr2 = std::move(ptr1); // ok

// ptr2 gets delete[]d at the end of scope

with custom deleter

using deleter = cleanup::function_deleter<void(void*), &free>;
using Res = resource<void, deleter::impl>;
Res ptr1{malloc(1024)};
Res ptr2; // ptr2{nullptr}

// ptr2 = ptr1; // error
ptr2 = std::move(ptr1); // ok

// ptr2 gets free()d at the end of scope

With your file descriptor RAII class

unique_ptr cannot do this - at least not without pointless allocation.

using deleter = cleanup::function_deleter<int(int), &close>;

using Res = resource<
	traits::handle_is_type<int, traits::nullable::yes, int, -1>,
	deleter::impl
>;

Res r1{open("/dev/random", O_RDONLY)};
Res r2; // initialized with -1

assert(*r2 == -1)
// r2 = r1; // error, but the copy policy can be convinced to use dup(2)
r2 = std::move(r1);

// r2 gets close(2)d.

lock_guard-like behaviour

The cleanup policy can also define initialize method.

template<typename T, typename Resource>
struct MutexLocker
{
	void initialize()
	{
		auto& full_type = static_cast<Resource&>(*this);
		full_type->lock();
	}

	void cleanup()
	{
		auto& full_type = static_cast<Resource&>(*this);
		full_type->unlock();
	}
};

And the usage:

using Res = resource<traits::reference<std::mutex>,MutexLocker>;
// reference trait is not nullable

std::mutex m;
Res r{m}; // m.lock() called

// Res r2 = r; // error
// Res r2 = std::move(r); // error

// m.unlock() called

Why? My unique_ptr and lock_guard are better/good enough?

Most likely you're right. This was a programming exercise.

License

If you really want to use this, look here.