groovy-stream post

from.groovy

import groovy.stream.Stream

// Repeat an object indefinitely
Stream s = Stream.from { 1 }
assert s.take( 5 ).collect() == [ 1, 1, 1, 1, 1 ]

// Use an Iterable
Stream s = Stream.from 1..3
assert s.collect() == [ 1, 2, 3 ]

// Use an iterator
def iter = [ 1, 2, 3 ].iterator()
Stream s = Stream.from iter
assert s.collect() == [ 1, 2, 3 ]

// Use a map of iterables
Stream s = Stream.from x:1..2, y:3..4
assert s.collect() = [ [x:1,y:3],[x:1,y:4],[x:2,y:3],[x:2,y:4] ]

limits.groovy

// Try and limit an endless Stream with a using block
Stream s = Stream.from { 1 } where { idx < 5 ?: STOP } transform { idx++ ; it } using idx:0

// The length of this is 1 greater than expected as transform is executed
// (and so idx is updated) AFTER the where condition has already passed the
// last element.
assert s.collect().size() == 6

maptransform.groovy

s = Stream.from a:1..2, b:3..4 transform { a + b }
assert s.collect() == [ 4, 5, 5, 6 ]

mapwhere.groovy

// Maps are passed as the delegate to where
Stream s = Stream.from a:1..2, b:3..4 where { ( a + b ) % 2 == 0 }
assert s.collect() == [ [a:1,b:3], [a:2,b:4] ]

stop.groovy

def x = 0
def eternal = [ hasNext:{ true }, next:{ x++ } ] as Iterator
// True whilst it < 5 otherwise, STOP
Stream s = Stream.from eternal where { it < 5 ?: STOP }
assert s.collect() == [ 0, 1, 2, 3, 4 ]

transform.groovy

Stream s = Stream.from 1..5 transform { it + 5 }
assert s.collect() == [ 6, 7, 8, 9, 10 ]

using.groovy

// Starting with idx:0, return elements with an index element before them
Stream s = Stream.from 'a'..'c' transform { [ idx++, it ] } using idx:0
assert s.collect() == [ [0,'a'], [1,'b'], [2,'c'] ]

where.groovy

Stream s = Stream.from 1..10 where { it % 2 == 0 }
assert s.collect() == [ 2, 4, 6, 8, 10 ]