[ << ] | [ < ] | [ Up ] | [ > ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |

#### 7.5.34.1 Creating hash tables

- Scheme Procedure:
**make-hash-table***[equal-proc hash-proc #:weak weakness start-size]* 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 than`equal?`

unless it is literally`string-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? `

as well. If that does not hold for
your `x` `y`)`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 section Weak References, for more
information on Guile’s built-in weak table support.

- Scheme Procedure:
**alist->hash-table***alist [equal-proc hash-proc #:weak weakness start-size]* As with

`make-hash-table`

, but initialize it with the associations in`alist`. Where keys are repeated in`alist`, the leftmost association takes precedence.

[ << ] | [ < ] | [ Up ] | [ > ] | [ >> ] | [Top] | [Contents] | [Index] | [ ? ] |

This document was generated on *April 20, 2013* using *texi2html 5.0*.