NoRewindIterator何时回退内部迭代器？ [英] When does the NoRewindIterator rewind the inner Iterator?

问题描述

通过它的名字，当PHP的 NoRewindIterator 倒带时，非常清楚：从不。

By its name it is perfectly clear when PHP's NoRewindIterator rewinds: never.

但有时，尤其是。从它延伸时，我问自己：它是否会倒带？它倒带一次吗？所以，如果我需要它，我是否需要实现（第一次）倒带，因为某些 Traversable 可能需要它？

But sometimes, esp. when extending from it, I ask myself: Does it ever rewind? Does it rewind once? So if I need it, do I need to implement the (first) rewind as some Traversable might require it?

我特别想知道这里的内部迭代器，所以 Iterator NoRewindIterator 类作为参数及其构造函数。

I specifically wonder about the inner iterator here, so the Iterator the NoRewindIterator class takes as parameter with its constructor.

例如：

$iterator = new SomeIterator(); // implements Iterator
$noRewind = new NoRewindIterator($iterator);
foreach ($noRewind as $value) {
    break;
}

将 $ iterator-> rewind（）从这里开始使用 $ noRewind 时从不调用？或者第一次调用一次 $ noRewind-> rewind（）被调用（例如在第一个 foreach 在示例中）。或者也许在构造？

Will $iterator->rewind() be never called when using $noRewind from here on? Or will it be called once for the first time $noRewind->rewind() is invoked (e.g. within the first foreach in the example). Or maybe on construct?

推荐答案

就像单独的类名一样（ NoRewindIterator ），手册中具体说明如下：

Like by the name of the class alone (NoRewindIterator), the manual has the following wording in specific:

NoRewindIterator - 此迭代器无法倒带。

NoRewindIterator - This iterator cannot be rewound.

对于具体方法：

NoRewindIterator :: rewind（） - 防止内部迭代器上的倒带操作。

NoRewindIterator::rewind() - Prevents the rewind operation on the inner iterator.

这意味着 Iterator :: rewind（）方法不会传递给内部迭代器。测试也显示了这个，这是一个我一直在运行的简单的（所有迭代器的代码都不是PHP的一部分在 Iterator Garden ）：

This implies that the Iterator::rewind() method is not passed through to the inner iterator. Tests also show this, here is a simple one I've been running (code of all iterators not part of PHP are in the Iterator Garden):

$iterator = new RangeIterator(1, 1);
$debug    = new DebugIteratorDecorator($iterator);
$noRewind = new NoRewindIterator($debug);

echo "first foreach:\n";

foreach ($noRewind as $value) {
    echo "iteration value: $value\n";
}

在此代码中，调试迭代器打印（回声）迭代信息fly：

In this code, the debug-iterator prints (echoes) iteration information on the fly:

first foreach:
Iterating (RangeIterator): #0 valid()
Iterating (RangeIterator): #0 parent::valid() is TRUE
Iterating (RangeIterator): #0 current()
Iterating (RangeIterator): #0 parent::current() is 1
iteration value: 1
Iterating (RangeIterator): #1 next()
Iterating (RangeIterator): #1 after parent::next()
Iterating (RangeIterator): #1 valid()
Iterating (RangeIterator): #1 parent::valid() is FALSE

如下所示， $ iterator-> rewind（）永远不会被调用。

As this shows, $iterator->rewind() is never called.

这也是有道理的在一个相关的问题： 为什么我必须回放IteratorIterator 。 NoRewindIterator 从 IteratorIterator 和不同扩展到它的父类 getInnerIterator（）方法返回 Iterator 而不是 Traversable 。

This also makes sense for the same reasons given in a related question: Why must I rewind IteratorIterator. The NoRewindIterator extends from IteratorIterator and different to it's parent class, the getInnerIterator() method returns an Iterator and not a Traversable.

此更改允许您在需要时初始化倒带：

This change allows you to initialize the rewind when you need to:

echo "\n\$calling noRewind->getInnerIterator()->rewind():\n";

$noRewind->getInnerIterator()->rewind();

echo "\nsecond foreach:\n";

foreach ($noRewind as $value) {
    echo "iteration value: $value\n";
}

再次显示调试输出：

$calling noRewind->getInnerIterator()->rewind():
Iterating (RangeIterator): #0 rewind()
Iterating (RangeIterator): #0 after parent::rewind()

second foreach:
Iterating (RangeIterator): #0 valid()
Iterating (RangeIterator): #0 parent::valid() is TRUE
Iterating (RangeIterator): #0 current()
Iterating (RangeIterator): #0 parent::current() is 1
iteration value: 1
Iterating (RangeIterator): #1 next()
Iterating (RangeIterator): #1 after parent::next()
Iterating (RangeIterator): #1 valid()
Iterating (RangeIterator): #1 parent::valid() is FALSE

了解这些细节后，确实允许创建一个 OneTimeRewindIterator 例如：

Knowing about these details then does allow to create a OneTimeRewindIterator for example:

/**
 * Class OneTimeRewindIterator
 */
class OneTimeRewindIterator extends NoRewindIterator
{
    private $didRewind = FALSE;

    public function rewind() {
        if ($this->didRewind) return;

        $this->didRewind = TRUE;
        $this->getInnerIterator()->rewind();
    }
}

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