为什么在迭代器上执行映射不会导致对其进行修改？

Question

> val textIt = text.split("\\s").iterator
> val upperIt = textIt.map(_.toUpperCase)
> textIt
res14: Iterator[String] = non-empty iterator

Why is textIt not empty? I would expect it to become an empty iterator due to map iterating over them. What is actually happening under the hood?

Answer 1

Method Iterator.map returns new Iterator object without traversing over it:

def map[B](f: A => B): Iterator[B] = new AbstractIterator[B] {
  def hasNext = self.hasNext
  def next() = f(self.next())
}

Iterating over textIt is performed when you iterate over upperIt .