Status: Passed, as amended here, Jun 89 X3J13
References: CLtL p.283
Edit history: Version 1, 20-Mar-89, by Moon
Version 2, 1-Jul-89, by Masinter (per Jun89 X3J13 amendments)
CLtL contradicts itself on the meaning of the :SIZE argument to
MAKE-HASH-TABLE. At the top of p.283, it says that the size is "the
maximum number of entries it can hold. Usually the actual capacity of
the table is somewhat less." At the bottom of the page it says "this
argument serves as a hint to the implementation of approximately how
many entries you intend to store." So does the :SIZE intended to be the
actual capacity of the table, or the amount of storage allocated to hold
the table. For example, if the implementation of hash tables is
designed for a loading of 65%, and the user specifies :SIZE 100, does
the table returned have space allocated for 100 entries, so that it
overflows and becomes bigger when 65 entries are inserted, or does the
table have space allocated for 154 entries, so that it overflows and
becomes bigger when 100 entries are inserted?
Believe the bottom of p.283 rather than the top. The :SIZE argument
is approximately the number of entries that can be inserted without
the table having to grow.
Keep the first and last sentences of the definition of :REHASH-THRESHOLD
(CLtL p. 284.) Replace the rest with:
"This can be a REAL between 0 and 1, inclusive, which is a hint to the
implementation of the maximum desired hash table occupancy level. An
implementation is permitted to ignore this argument."
Remove the second complete paragraph of CLtL p. 283. It's too implementa-
tion-dependent. Clarify the implementation is not necessarily an actual
hash table of any particular hashing technique.
The bottom of p.283 is user-oriented, the top is implementation-oriented.
User-oriented seems more appropriate.
Symbolics Genera 7.4 adheres to HASH-TABLE-SIZE:INTENDED-ENTRIES.
Other implementations were not surveyed.
Cost to Implementors:
At worst adding a multiplication to MAKE-HASH-TABLE.
Cost to Users:
Probably none, but it is hard to predict.
Cost of non-adoption:
Implementations will probably vary in which of the two interpretations
they believe. The language standard will not be self-consistent.
None of any significance.
More self-consistent language.