Carrying around a fat deleter in every pointer instance is what I consider a no-go.
Nevertheless, there are many scenarios where it would be important. And in keeping with the well-understood interfaces of shared_ptr and unique_ptr, I strongly suggest it would be demanded by the community. By all means have a specialisation of the deleter's implementation for this case - it's a useful optimisation. Some scenarios where you'd want a "fat" deleter: 1. you need to return objects to a pool 2. you need to release a semaphore 3. you need to post a notification on a message queue 4. deletion is necessarily constrained by accessing a mutex. 5. the deleter isn't actually fat - it's a stateless class such as std::default_delete! I still agree that a type-erased-deleter-unique_ptr is useful. One that could only accept a function pointer as the deleter would be surprising to anyone who has had contact with unique_ptr or shared_ptr. I could not support this constraint. On 21 March 2017 at 16:00, Andrey Semashev via Boost <boost@lists.boost.org> wrote:
On 03/21/17 17:53, Richard Hodges via Boost wrote:
A poly_deleter really should not hold just a function pointer as a deleter. The custom deleter may be any function, containing any amount of state (it could for example be returning resources to a memory pool, or managing a semaphore).
fixing the deleter type at `void (*)(void*)` is a no-go. It's not useful.
If you want something more generic then just use std::function as a deleter. It's been mentioned earlier in the thread.
Personally though, I don't remember needing anything more elaborate than a `void (*)(void*)` function or similar. Probably because if I need something more advanced, I'll likely choose a virtual destructor or shared_ptr or intrusive_ptr. Carrying around a fat deleter in every pointer instance is what I consider a no-go.
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