Alias SharedPtr.WeakType

Weak pointer

struct SharedPtr
{
  // ...
  alias WeakType = SharedPtr!(_Type,_DestructorType,_ControlType,true);
  // ...
}

SharedPtr.WeakType is a smart pointer that holds a non-owning ("weak") reference to an object that is managed by SharedPtr. It must be converted to SharedPtr in order to access the referenced object.

SharedPtr.WeakType models temporary ownership: when an object needs to be accessed only if it exists, and it may be deleted at any time by someone else, SharedPtr.WeakType is used to track the object, and it is converted to SharedPtr to assume temporary ownership. If the original SharedPtr is destroyed at this time, the object's lifetime is extended until the temporary SharedPtr is destroyed as well.

Another use for SharedPtr.WeakType is to break reference cycles formed by objects managed by SharedPtr. If such cycle is orphaned (i,e. there are no outside shared pointers into the cycle), the SharedPtr reference counts cannot reach zero and the memory is leaked. To prevent this, one of the pointers in the cycle can be made weak.