Iterator Utils for Groovy

Iterator Utils for groovy is a package inspired by python iterutils, in turn inspired by constructs from APL, Haskell, and SML. It provides tools for doing lazy evaluation on any collection or stream that implements the Iterable or Iterator interface.

Iterables, Iterators, And Collections

The Iterable interface was introduced in Java 1.5 and was added all the collection datatypes. It defines a single method, iterator(), that returns an iterator. Groovy conveniently adds an iterator method to the Iterator class (which just returns itself), and although it doesn't make Iterator formally implement Iterable, it effectively does using groovy duck typing.

This means that Iterators and Iterables can be used interchangably, using the iterator method to on either an Iterable or Iterator to get an Iterator. All the IteratorUtils methods can take an Iterator or an Iterable.

Examples

import static ca.redtoad.util.IteratorUtils.*

// squares of "infinite" set of numbers calculated lazily when take called
def numbers = count()
def squareNumbers = map({x -> x * x}, numbers)
assert take(4, squareNumbers).toList() == [0, 1, 4, 9]

// substring on number doesn't fail since it's never evaluated
def list = ["string", "string", "string", 1.0]
def subStrings = map({x -> x.substring(0, 3)}, list)
assert take(3, subStrings).toList() == ["str", "str", "str"]

See Also

http://groovy.codehaus.org/Iterator+Tricks