23 Sep
2011
23 Sep
'11
2:18 p.m.
Sebastian Redl wrote:
On 23.09.2011 13:43, Olaf van der Spek wrote:
Hi,
I was wondering why shared_ptr/array include both a ptr to the control block and a ptr to the data (ptr) in the class itself. I assume it's for performance reasons, but I didn't find anything about that in the docs.
It's for aliasing. You can have a shared_ptr that points to a subobject of the object controlled by the control block.
It's true that the separate pointer enables aliasing, but this is not the original reason for its existence. It supports pointer conversions (shared_ptr<T> converts to shared_ptr<U> when T* converts to U*.) shared_array doesn't technically need aliasing or conversions, its implementation just mirrors shared_ptr.