Status: Passed, as amended, Mar 89 X3J13 (by vote of 17-0)
References: Hash-tables (Chapter 21 of CLtL)
Edit History: 13-Sept-88, version 1 by Walter van Roggen
13-Oct-88, version 2 by Walter van Roggen
05-Apr-89, version 3 by Pitman (changes per x3J13)
There are many characteristics of hash-tables which are specified upon
creation but are not accessible afterwards.
Add the following functions to the language:
Returns the current rehash size of a hash table.
Returns the current rehash threshold of a hash table.
Returns the current size of a hash table.
Returns the test used for comparing keys in the hash table.
By default the value will be EQL.
Define that the results of HASH-TABLE-REHASH-SIZE,
HASH-TABLE-REHASH-THRESHOLD, and HASH-TABLE-SIZE are suitable
for use in a call to MAKE-HASH-TABLE in order to produce a hash
table with state corresponding to the current state of the hash
Clarify that the result of HASH-TABLE-TEST is always a symbol
naming a function rather than the function itself if the test
is one of those defined by this standard. (Implementations which
provide additional tests for hash tables may determine how this
function relates to such extended tests.)
VAX LISP and Lucid 3.0 implement the proposal.
Cost to Implementors:
Most of these should be trivial to implement, since the information
must be present for nearly all types.
Cost to Users:
None. This is an upward-compatible extension.
Cost of Non-Adoption:
The benefits would not be available in a portable fashion.
Programs would be able to access useful information otherwise hidden.
For example, it would allow programs to gain statistics about hash
table usage that might enable better tuning.
None of these are required to be SETF'able, though some might be
reasonable implementation-dependent extensions. Including such
modification abilities might constrain some implementations unduly.
This first appeared in ">GLS>clarifications.text" of 12/06/85.