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 they 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 of the higher generation is required to remove the pointer. Note that by default the system does not automatically GC the blocking generation or higher.
The weakness state of an array can be changed many times.
In all implementations,
array
must not be a displaced array, and the
array-element-type
of array must be
t
.
In 64-bit LispWorks, an additional requirement is that array must be an adjustable array.
set-array-weak
can be called at any moment.
Note: An array can be made weak at creation time using the
:weak
argument to make-array.