Composable Iterators with Guava and Groovy

iterators.groovy

@Grab( 'com.google.guava:guava:15.0' )
import com.google.common.collect.Iterators

Iterator.metaClass {
    leftShift = { Iterator b ->
        Iterators.concat( delegate, b )
    }
    leftShift = { Iterable b ->
        Iterators.concat( delegate, b.iterator() )
    }
}

def a = [ 1, 2, 3 ].iterator()
def b = [ 4, 5, 6 ].iterator()
def c = [ 7, 8, 9 ].iterator()

def composed = a << b << c << [ 'a', 'b', 'c' ]

assert composed.collect() == [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 'a', 'b', 'c' ]