Create and answer a new hash table with equal-proc as the equality function and hash-proc as the hashing function.
By default, equal-proc is
equal?
. It can be any two-argument procedure, and should answer whether two keys are the same for this table's purposes.My default hash-proc assumes that
equal-proc
is no coarser thanequal?
unless it is literallystring-ci=?
. If provided, hash-proc should be a two-argument procedure that takes a key and the current table size, and answers a reasonably good hash integer between 0 (inclusive) and the size (exclusive).weakness should be
#f
or a symbol indicating how “weak” the hash table is:
#f
- An ordinary non-weak hash table. This is the default.
key
- When the key has no more non-weak references at GC, remove that entry.
value
- When the value has no more non-weak references at GC, remove that entry.
key-or-value
- When either has no more non-weak references at GC, remove the association.
As a legacy of the time when Guile couldn't grow hash tables, start-size is an optional integer argument that specifies the approximate starting size for the hash table, which will be rounded to an algorithmically-sounder number.
By coarser than equal?
, we mean that for all x and
y values where (
equal-proc x y)
,
(equal?
x y)
as well. If that does not hold for
your equal-proc, you must provide a hash-proc.
In the case of weak tables, remember that references above
always refers to eq?
-wise references. Just because you have a
reference to some string "foo"
doesn't mean that an association
with key "foo"
in a weak-key table won't be collected;
it only counts as a reference if the two "foo"
s are eq?
,
regardless of equal-proc. As such, it is usually only sensible
to use eq?
and hashq
as the equivalence and hash
functions for a weak table. See Weak References, for more
information on Guile's built-in weak table support.