Creates and returns a new hash table. The keywords are as follows:

:test

Indicates what kind of test to use. Only eq, eql, equal, and equalp are currently supported.

:size

A hint as to how many elements will be put in this hash table.

:rehash-size

Indicates how to expand the table when it fills up. If an integer, add space for that many elements. If a floating point number, which must be greater than 1.0, multiple the size by that amount.

:rehash-threshold

Indicates how dense the table can become before forcing a rehash. Can be any positive number <= to 1, with density approaching zero as the threshold approaches 0. Density 1 means an average of one entry per bucket.

Extensions:

:lock

The specialized type of lock used to synchronize access to the hash table, or nil for no synchronization. The valid lock types are: :normal, :recursive, or :error-check. The default lock type is :recursive. A hash table without a lock for synchronization may be appropriate if the table is known to be used by a single thread, or if synchronization is already handled by another lock.

:weak-p

If t, do not keep entries if the key would otherwise be garbage, currently unimplemented.