A non-displaced array, with array-element-type t .
If weakp is non- nil , the array is made weak. If weakp is nil , the array is made non-weak.
By default, arrays are non-weak, and keep alive all the objects that are stored in them. A weak array may remove a pointer if the object that it points to is not pointed to from somewhere else. When a pointer is removed like this, it is replaced in array with nil .
Pointers are replaced by nil after a garbage collector operation that identifies that they can be replaced. This means that if the object that is pointed to has been promoted to a higher generation, a garbage collection (mark and sweep) of the higher generation is required to remove the pointer. Note that by default the system does not automatically call mark-and-sweep on generation 2 or higher.
The weakness state of an array can be changed many times.
array must not be a displaced array. The array-element-type of array must be t .