std::unique_ptr and custom allocator deleter

Question

I am trying to use std::unique_ptr with custom memory allocators. Basically, I have custom allocators that are subclasses of IAllocator,

Answer 1

T* doesn't contain such information, neither unique_ptr knows about the size of the array (since it uses directly a delete [] as you stated). You could let the T be a unique_ptr<T> to manage the destruction automatically but this could not be possible if the whole contiguous T* is managed by a memory allocator (and not a single T* object). Eg:

unique_ptr<unique_ptr<Foo>[]> data;
data.reset(new unique_ptr<Foo>[50]);
data[0].reset(new Foo());

Answer 2

Yes, there most certainly is a better way:
Use a maker-function.

template<class T, class A> std::unique_ptr<T[], MyArrDeleter>
my_maker(size_t count, A&& allocator) {
    return {somePtr(allocator.AllocArray<T>(count), MyArrDeleter(allocator, count)};
}

auto p = my_maker<T>(42, allocator);