Iterable & Iterator

给我写信
GitHub

Scala

Iterable与Iterator的区别

简而言之，Iterator有状态，而Iterable无状态。看看API doc是怎么说的。

Iterable :

A base trait for iterable collections.

This is a base trait for all Scala collections that define an iterator method to step through one-by-one the collection's elements. [...] This trait implements Iterable's foreach method by stepping through all elements using iterator.

Iteraotor :

Iterators are data structures that allow to iterate over a sequence of elements. They have a hasNext method for checking if there is a next element available, and a next method which returns the next element and discards it from the iterator.

An iterator is mutable: most operations on it change its state. While it is often used to iterate through the elements of a collection, it can also be used without being backed by any collection (see constructors on the companion object).

使用一个Iterator实例：可以迭代到某一处时停下来，然后随后继续迭代下去。
使用一个Iterable实例：如果迭代到某一处停下来，随后想继续迭代时就不可能了，只能从头开始迭代。
此外，Iterator 扩展了 TraversableOnce，而Iterable没有。

Iterator 的潜在危险

由于Iterator有状态的，因此在使用时可能会隐藏着地雷，请参考 Iterators in Scala: glory and danger .