• maphash function hash-table → nil

• function - a designator for a function of two arguments, the key and the value.
• hash-table - a hash table.

Iterates over all entries in the hash-table. For each entry, the function is called with two arguments--the key and the value of that entry.

The consequences are unspecified if any attempt is made to add or remove an entry from the hash-table while a maphash is in progress, with two exceptions: the function can use can use setf of gethash to change the value part of the entry currently being processed, or it can use remhash to remove that entry.

(defparameter *table* (make-hash-table)) 

→

*TABLE*



(dotimes (i 10) (setf (gethash i *table*) i)) 

→

NIL 



(let ((sum-of-squares 0)) 
  (maphash #'(lambda (key val) 
               (let ((square (* val val))) 
                 (incf sum-of-squares square) 
                 (setf (gethash key *table*) square)))


table*) 




  sum-of-squares) 

→

285 



(hash-table-count *table*) 

→

10 



(maphash #'(lambda (key val) 
             (when (oddp val) (remhash key *table*)))


table*) <r>NIL </r>




(hash-table-count *table*) 

→

5 



(maphash #'(lambda (k v) (print (list k v))) *table*)

▷

(0 0)
(8 64) 
(2 4) 
(6 36) 
(4 16) 

→

NIL </blockquote>



====Side Effects====
None, other than any which might be done by the function.



====Affected By====
None.



====Exceptional Situations====
None.



====See Also====


 Macro LOOP

 Macro WITH-HASH-TABLE-ITERATOR,




{\secref\TraversalRules}



====Notes====
None.



\issue{MAPPING-DESTRUCTIVE-INTERACTION:EXPLICITLY-VAGUE}