Sets the weakness state of hash-table. Value may be:
-- An entry is kept if there is a pointer to the value from another object.
-- An entry is kept if there is a pointer to the key from another object.
-- An entry is kept if there are pointers to both the key and the value.
-- An entry is kept if there is a pointer to either the key or the value.
-- Make the hash-table non-weak. All entries are kept.
Entries that can be removed are removed after a garbage collector operation which identifies that they can be removed. This means that if the relevant object(s) (the key or the value) have been promoted to a higher generation, a garbage collection (mark and sweep) of the higher generation is required to remove them from the table. Note that by default the system does not automatically call
on generation 2 or higher.