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9.3.3 Miscellaneous operations on collection

Generic function: size-of coll
Returns the number of elements in the collection. Default method iterates over the collection to calculate the size, which is not very efficient and may diverge if the collection is infinite. Some collection classes overload the method for faster calculation.

Generic function: lazy-size-of coll
Returns either the size of the collection, or a promise to calculate it. The intent of this method is to avoid size calculation if it is expensive. In some cases, the caller wants to have size just for optimization, and it is not desirable to spend time to calculate the size. Such caller uses this method and just discards the information if it is a promise.

Generic function: coerce-to class coll
Convert a collection coll to another collection which is an instance of class. If coll is a sequence and class is a sequence class, the order is preserved.

(coerce-to <vector> '(1 2 3 4))
  => #(1 2 3 4)

(coerce-to <string> '#(#\a #\b #\c))
  => "abc"

This document was generated by Ken Dickey on November, 28 2002 using texi2html