7.6 Hash table extensions

7.6.2 Reference pages

hash-table-rehash-size Function

hash-table-rehash-threshold Function

hash-table-size Function

hash-table-test Function

Syntax:hash-table-rehash-size hash-table

Syntax:hash-table-rehash-threshold hash-table

Syntax:hash-table-size hash-table

Syntax:hash-table-test hash-table

These functions access components of a hash table created by the Common Lisp functionmake-hash-table:

You can use the Common Lisp macrosetf with the functionshash-table-rehash-size,hash-table-rehash-threshold, andhash-table-test to update the corresponding hash table component; you cannot update the:size component in this way.

See Also: rehash;make-hash-table (in CLtL2)

rehash Function

Syntax:rehash hash-table&optional new-option

The functionrehash either changes the size of the specified hash table or redistributes the keys as evenly as possible over the range of index values. This redistribution of keys, or rehashing, can improve the performance of hashing functions by reducing the number of probes that are necessary to find an element in the table.

The optional new-option argument has the following effects:

When the number of items being entered into a hash table exceeds the table's rehash threshold,rehash is called internally with new-option set tot to increase the size of the table.

Note: Hash tables of typeeq oreql might need to be rehashed after any relocating garbage collection, including any ephemeral scavengings. Rehashing is advised because the addresses of the keys entered in the table can change after a relocation. This kind of rehashing is not necessary for any table whose keys are all either symbols, fixnums, or characters.

See Also:make-hash-table (in CLtL2)

The Advanced User's Guide - 9 SEP 1996

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