Typedef a shared_ptr type with a static custom deleter, similar to unique_ptr

Question

I have read through many questions on SO on custom deleter for shared_ptr and unique_ptr, and the difference between the two. But, I still haven\'t

Answer 1

A typedef is a static, compile-time feature.

A deleter passed to a shared_ptr is a dynamic, run-time property. The deleter is "type-erased" and is not part of the shared_ptr interface.

Therefore you can't declare a typedef to represent an alternative deleter, you just pass one to the constructor.

What would be the best way to achieve the same kind of usage as with the unique_ptr example of above.

You could use functions to create the resources and return them in a shared_ptr

shared_ptr create_sdl_surface(const char* s)
{
  return shared_ptr(IMG_load(s), SDL_FreeSurface);
}

But I would have those functions return a unique_ptr instead, which can be converted to shared_ptr, as below.

I would get rid of the macro and do something like this:

// type with overloaded functions for freeing each resource type
struct SDL_deleter
{
  void operator()(SDL_Surface* p) const { if (p) SDL_FreeSurface(p); }
  void operator()(SDL_RWops* p) const { if (p) SDL_RWclose(p); }
  // etc.
};

// a unique_ptr using SDL_deleter:
template
  using SDL_Ptr = std::unique_ptr;

// typedefs for the common ptr types:
using SurfacePtr = SDL_ptr;
using RWopsPtr = SDL_ptr;
// etc.

To answer the shared_ptr part of your question, define functions that create resources and return them in a SDL_ptr:

SurfacePtr createSurface(const char* s) { return SurfacePtr(IMG_load(s)); }
RWopsPtr createRWops([...]) { return RWopsPtr([...]); }
// etc.

Then you can easily create a shared_ptr from the result of those functions:

shared_ptr s = createSurface("image.png");

The shared_ptr automatically acquires the right deleter from the unique_ptr.