Question

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?

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.).

Answer 1

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.

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.

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.

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.

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.