Lazy implementation of collect for Groovy

lazyCollectImpl.groovy

class LazyCollectList extends AbstractList {
    
    private Closure collectClosure
    
    private List backingList
    
    private Map cached = [:]
    
    def get(int i) {
        if(!cached.containsKey(i)) {
            cached[i] = collectClosure(backingList[i])    
        }
        
        cached[i]
    }
    
    int size() {
        backingList.size()
    }   
}

List.metaClass.lazyCollect = { Closure cl ->
    new LazyCollectList(collectClosure: cl, backingList: delegate)
}

assert [1, 2, 3].lazyCollect{ it * 2 } == [2, 4, 6]
def collectWasCalled = false
[1, 2, 3].lazyCollect{ collectWasCalled = true }
assert collectWasCalled == false