为什么我必须回放IteratorIterator [英] Why must I rewind IteratorIterator

问题描述

$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（） ，然后 $ iterIter-> valid（）为真。我很好奇为什么要调用rewind（）。我想它有充分的理由，但我希望它只是在内部迭代器处于的任何状态下开始迭代，并在开始迭代之前将其作为回退选项。

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.

调用next（）似乎也将其置于有效状态（虽然它前进到下一个位置，表明它之前处于第一个位置）。

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()); 

再次，我很好奇为什么我需要调用rewind（），尽管内部迭代器在一个有效的状态。

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

推荐答案

使用新的迭代器，位置未初始化，只是出于性能原因，你可以叠加迭代器在其他迭代器的顶部，如果所有这些迭代器都会在构造期间倒回会产生一些性能影响，另外一些迭代器可能会在构造函数执行后更改它们的第一个值 - 这对迭代器来说是未知的。

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.

迭代器通常由foreach（）执行，它首先执行倒带（）...

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

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