Re: [boost] [smart_ptr] Is there any interest in unique_ptr with type erased deleter?

Subject: Re: [boost] [smart_ptr] Is there any interest in unique_ptr with type erased deleter?
From: Richard Hodges (hodges.r_at_[hidden])
Date: 2017-03-21 14:53:33

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.

On 21 March 2017 at 15:33, Andrey Semashev via Boost <boost_at_[hidden]>
wrote:

> On 03/21/17 16:33, Andrey Davydov wrote:
>
>> On Tue, Mar 21, 2017 at 4:11 PM, Andrey Semashev
>> <andrey.semashev_at_[hidden] <mailto:andrey.semashev_at_[hidden]>> wrote:
>>
>>       struct poly_deleter
>>       {
>>         template< typename T >
>>         poly_deleter(T* p) : m_p(p), m_delete(&poly_deleter::do_delete<
>> T >)
>>         {
>>         }
>>
>>         void operator() (void*) const noexcept
>>         {
>>           m_delete(m_p);
>>         }
>>
>>       private:
>>         template< typename T >
>>         static void do_delete(void* p) noexcept
>>         {
>>           delete static_cast< T* >(p);
>>         }
>>
>>         void* m_p;
>>         void (*m_delete)(void*);
>>       };
>>
>>     This will work even if you form std::unique_ptr<void, poly_deleter>
>>     (i.e. don't have a universal base class).
>>
>> Your poly_deleter implementation is the same as I used inside my smart
>> pointer implementation, but there is an issue with std::unique_ptr<T,
>> poly_deleter>, namely it is not constructible from std::unique_ptr<T,
>> std::default_delete<T>> because poly_deleter must capture pointer and so
>> it is not constructible from std::default_delete.
>>
>
> I think that problem can be solved by make_poly_unique or a conversion
> helper function. Hardly a whole new smart-pointer is an adequate solution.
>
>
>
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