Re: Making all Traversables an Iterator or IteratorAggregate

Hi Nikita, Den 2020-06-19 kl. 12:32, skrev Nikita Popov:

On Tue, Jun 9, 2020 at 3:33 PM Nikita Popov <nikita.ppv@gmail.com> wrote:

On Tue, May 12, 2020 at 10:26 AM Nikita Popov <nikita.ppv@gmail.com> wrote:

On Wed, Mar 11, 2020 at 10:50 AM Nikita Popov <nikita.ppv@gmail.com> wrote:

Hi internals, Userland classes that implement Traversable must do so either through Iterator or IteratorAggregate. The same requirement does not exist for internal classes: They can implement the internal get_iterator mechanism, without exposing either the Iterator or IteratorAggregate APIs. This makes them usable in get_iterator(), but incompatible with any Iterator based APIs.

This should have said: "This makes them usable in foreach(), but incompatible with any Iterator based APIs." A lot of internal classes do this, because exposing the userland APIs is

simply a lot of work. I would like to add a general mechanism to make this simpler: https://github.com/php/php-src/pull/5216 adds a generic "InternalIterator" class, that essentially converts the internal get_iterator interface into a proper Iterator. Internal classes then only need to a) implement the IteratorAggregate interface and b) add a getIterator() method with an implementation looking like this: // WeakMap::getIterator(): Iterator ZEND_METHOD(WeakMap, getIterator) {

     if (zend_parse_parameters_none() == FAILURE) {
         return;
     }
     zend_create_internal_iterator_zval(return_value, ZEND_THIS);

} This allows internal classes to trivially implement IteratorAggregate, and as such allows us to enforce that all Traversables implement Iterator or IteratorAggregate.

Does anyone have thoughts on this change? Mostly this is a feature for extensions, but also user-visible in that a bunch of classes will switch from being Traversable to being IteratorAggregate. We may also want to convert some existing Iterators to IteratorAggregates. For example SplFixedArray currently implements Iterator, which means that it's not possible to have nested loops over SplFixedArray. We could now easily fix this by switching it to use IteratorAggregate, which will allow multiple parallel iterators to work on the same array. Of course, there is BC break potential in such a change. There's some bikeshed potential here regarding the class name. I picked "InternalIterator" as an iterator for internal classes, but "internal iteration" is also a technical term (the opposite of "external iteration"), so maybe that name isn't ideal.

Unfortunately this bikeshed remains unpainted... The proposed names were: 1. InternalIterator 2. ZendIterator 3. IteratorForExtensionClassImplementations 4. EngineIterator I'm somewhat partial to the third option, with a less verbose name: IteratorForExtensions.

I went ahead and changed the implementation to use IteratorForExtensions. Is anyone overly unhappy with that one? @Michal: "ExtensionsIterator" to me sounds like an iterator that iterates over extensions. Regards, Nikita

I'm actually in favour of the term InternalIterator like you first proposed. Internal and external iteration is clearly something different, so no need due to these to shy away here ;-) And today this iterator will be for extensions, but if somehow that would change in the future (which I don't think), option 3 is not ideal. r//Björn L