Re: Yet Another Container: DynamicArray

From: Gavin Lambert (boost_at_[hidden])
Date: 2020-01-29 05:55:22

On 29/01/2020 18:39, Glen Fernandes wrote:
>> A std::unique_ptr<T[], D> stores a D::pointer.
>>
>> In our case, D is alloc_deleter<T[], A> and its   ::pointer is an
>> alloc_ptr<T[], Allocator>.
>>
>> This alloc_ptr<T[], Allocator>  stores an A::pointer and a size_t.
>>
>>> This seems incompatible with what you're saying above.
>>
>> It isn't.
>>
>>   > (There is also no mention of ptr() or size() there.)
>>
>> It specifies that the ::pointer is an 'unspecified' pointer-like type.
>> I forgot to document that on this unspecified pointer type one can use
>> .ptr() to get the Allocator::pointer and .size() to get the size.
> 
> Basically, a unique_ptr result from an allocate_unique<T[]>(a, n)
> _has_ to store the n somewhere in the unique_ptr because it needs to
> know how many objects to destroy and what size storage to deallocate.
> 
> I also provide access for you to get that n.  (I just forgot to put it
> in the documentation).

Does it also implicitly decay to a T*?

(I did have a look at 
https://github.com/boostorg/smart_ptr/blob/master/include/boost/smart_ptr/allocate_unique.hpp 
but I don't see any `operator T*`, which is what I'd expect.)

If not, that seems like it'd make it hard to pass to something expecting 
a raw pointer (eg. as method argument, or to construct a std::span).

Or unless you know about the extra undocumented .ptr() indirection 
requirement.