[swift-evolution] [Proposal] Change some collection iterators to use custom types instead of IndexIterator<T>

[Xiaodi Wu]

(thumbs up)


On Fri, Jul 22, 2016 at 4:35 PM, Michael Gottesman via swift-evolution <
swift-evolution at swift.org> wrote:

> Hello everyone!
>
> Iterators are very important for performance since we use them for for
> loops. By default collections if they do not provide a custom iterator use
> IndexingIterator as an iterator. IndexingIterator, while only supporting
> forward movement, is based on indices which possess the ability to go
> backwards and forwards. For some indices, backwards iteration adds
> unnecessary cost/complexity.
> In order to preserve future flexibility, we want to change certain of the
> types to use custom types that are essentially just IndexingIterator<T>.
> Then later on when we want to implement these optimizations, we can do it
> on the custom type underneath the hood without changing the API/ABI.
>
> The reason I use the phrase "some iterators" is that I already know that
> we definitely want to do this for StringCharacterView but there are
> potentially other containers in the standard library that this could apply
> to. I still need to audit these containers for potential applications. That
> being said given the place where we are in the schedule, I think it is
> important to start the discussion about the general concept and after I
> audit the various containers, I will post an update.
>
> Thoughts, flames, etc?
> Michael
>
> https://bugs.swift.org/browse/SR-1961
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