为什么我必须重绕IteratorIterator(Why must I rewind IteratorIterator)

为什么我必须重绕IteratorIterator(Why must I rewind IteratorIterator) $arrayIter = new ArrayIterator( array(1, 2) ); $iterIter = new IteratorIterator($arrayIter); var_dump($iterIter->valid()); //false var_dump($arrayIter->valid()); //true

如果我第一次调用$ iterIter-> rewind（） ，那么$ iterIter-> valid（）是真的。 我很好奇为什么它需要rewind（）被调用。 我想这是有很好的理由的，但我会期望它只是在内部迭代器所处的状态下开始迭代，并且在开始迭代之前将它作为倒回的选项。

调用next（）似乎也将其置于“有效”状态（尽管它进入下一个位置，表明它以前处于第一个位置）。

$arrayIter = new ArrayIterator(array(1,2)); $iterIter = new IteratorIterator($arrayIter); $iterIter->next(); var_dump($iterIter->valid());

同样，我很好奇为什么我需要调用rewind（），尽管内部迭代器处于有效状态。

$arrayIter = new ArrayIterator( array(1, 2) ); $iterIter = new IteratorIterator($arrayIter); var_dump($iterIter->valid()); //false var_dump($arrayIter->valid()); //true

If I first call $iterIter->rewind(), then $iterIter->valid() is true. I'm curious why it requires that rewind() be called. I imagine there's good reason for it, but I would have expected it to simply start iteration at whatever state it's inner iterator is in, and leave it as an option to rewind before beginning iteration.

calling next() also seems to put it in a "valid" state(although it advances to the next position, suggesting it was previously at the first position).

$arrayIter = new ArrayIterator(array(1,2)); $iterIter = new IteratorIterator($arrayIter); $iterIter->next(); var_dump($iterIter->valid());

Again, I'm curious why I need to call rewind(), despite the inner iterator being in a valid state.

最满意答案

使用新的迭代器时，位置不会被初始化，只是出于性能原因，您可以将迭代器叠加在其他迭代器之上，如果它们在构建过程中都会倒回会对性能产生影响，另外一些迭代器可能会在更改其第一个值之后构造函数被执行 - 迭代器未知。

迭代器通常由foreach（）执行，foreach（）首先执行倒回（）。

With a fresh iterator the position isn't initialized, simply for performance reason, you can stack iterators on top of other iterators, if all of them would rewind during construction there would be some performance impact, additionally some iterators might change their first value after the constructor was executed - which is unknown to iterators further out.

Iterators are usually executed by foreach() which does a rewind() first ...