为什么我必须倒带 IteratorIterator

Why must I rewind IteratorIterator(为什么我必须倒带 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

如果我先调用$iterIter->rewind()，那么$iterIter->valid() 为真.我很好奇为什么它需要调用 rewind() .我想这是有充分理由的，但我希望它只是在其内部迭代器所处的任何状态下开始迭代，并在开始迭代之前将其作为一个选项来回退.

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(尽管它前进到下一个位置，表明它之前位于第一个位置).

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()，尽管内部迭代器处于有效状态.

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，位置不会被初始化，出于性能原因，您可以将迭代器堆叠在其他迭代器之上，如果所有迭代器在构造会有一些性能影响，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 - 这对于更远的迭代器是未知的.

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 rewind() ...

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

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