PHP - 使用迭代器的原因? [英] PHP - Reasons to use Iterators?

问题描述

我今天仔细阅读手册并注意到各种迭代器.在我看来，它们似乎都毫无意义；除非您更喜欢它们的语法，或者不知道如何编写递归函数，否则我看不出使用它们的理由.是否有任何理由在 PHP 中使用内置迭代器而不是编写循环或创建递归方法?

I was perusing the manual today and noticed the various iterators. To me, it seems like they are all somewhat pointless; I don't see a reason to use them unless you prefer their syntax, or don't know how to write a recursive function. Are there any reasons to use built-in iterators in PHP over just writing a loop or making a recursive method?

我只是在寻找事实的回应，而不是主观的偏好(即:我不在乎你认为它更可读"还是更面向对象"，我想知道它们是否更快，提供滚动您自己的等时无法实现的功能.

I'm only looking for factual responses, not subjective preferences (ie: I don't care if you think it's more "readable" or "more object-oriented", I want to know if they're faster, offer functionality that can't be achieved when rolling your own, etc.).

推荐答案

我认为主要原因是多功能性.它们不会使事情更具可读性，您可以完成 spl 迭代器 用一个简单的 foreach 来做.

I believe the main reason is versatility. They don't make things more readable and you can accomplish most of what the spl iterators do with a simple foreach.

但迭代器可以作为一种压缩循环或循环源，您可以传递它.您可以拥有比列表/数组更多样化的数据源.真正的优势是您可以包装或堆叠它们以进行聚合.

But iterators can serve as sort of a compacted loop or loop source that you can pass around. You can have more diverse data sources than just a list/array. And the real advantage is that you can wrap or stack them for aggregation.

命名有点不明显，但我想你可以使用 AppendIterator 来例如，结合文件名的静态列表和 DirectoryIterator 的结果.或者以其他方式将其包装在 LimitIterator 中，而不是将其硬接线到 for 条件.所有这些都是非常基本的功能，可以在 foreach 中手动完成.但至少 RegexIterator 和 FilterIterator 似乎适合降低一些复杂性.

The naming is somewhat unobvious, but I guess you could use the AppendIterator to for example combine a static list of filenames and the result of a DirectoryIterator. Or otherwise wrap that in a LimitIterator instead of hardwiring that into a for condition. All of these are pretty basic features and can be done manually in a foreach. But at least RegexIterator and FilterIterator seem suitable to reduce some complexity.

但归根结底，这确实是一种风格选择.如果您有遍历某些东西的自定义对象(例如，可以指向真实文件或数据库条目的 VFS 对象)，那将是最有意义的.但即便如此，您也可以 iterator_to_array 转换这样的列表，并使用普通的 foreach-over-array.

But in the end it's really a stylistic choice. It would make most sense if you have custom objects which traverse something (for example a VFS object which can either point to real files or database entries). But even then you could just iterator_to_array convert such a list, and use a normal foreach-over-array.

唯一需要选择迭代器的情况是数据源的大小不受限制.foreach 中使用的展开数组比可以逐个检索元素的迭代器消耗更多的内存.

The only case were it is really imperative to prefer iterators were if the data source is unlimited in size. Unfolded arrays for use in a foreach can consume more memory than an iterator which can retrieve element by element.

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