[swift-users] Comprehensive documentation for Collection?

Howard Lovatt howard.lovatt at gmail.com
Sat Dec 16 00:05:51 CST 2017

It’s a problem with Apple documentation. swiftdoc.org does list the associated types, but is no longer maintained :(. 

-- Howard.

> On 16 Dec 2017, at 1:17 pm, Nevin Brackett-Rozinsky via swift-users <swift-users at swift.org> wrote:
> In Xcode if I write,
> extension Collection {
>     var secondIndex: Index { return index(after: startIndex) }
> }
> and then option-click on “Index”, it shows “associatedtype Index : Comparable” followed by a description. Is this documented somewhere?
> When I look at the documentation for Collection on developer.apple.com there is no mention of an Index associated type. I also don’t see it in The Swift Programming Language.
> If someone didn’t already know Collection.Index exists, how would they be expected to learn of it? And if they didn’t know it must be Comparable how would they learn that?
> Also, are there any semantic requirements on Collection.Index, for example is it required that “idx < index(after: idx)” must evaluate to true for any valid index “idx”?
> • • •
> On a somewhat related note, the “indices” property of Collection has a discussion section visible by option-clicking in Xcode or by looking at the documentation for it on developer.apple.com.
> And that discussion recommends against iterating over “indices” when mutating a collection, because “indices” could hold a strong reference to the collection and thus create an unexpected copy. Instead one should manually advance from startIndex to endIndex in a while loop.
> Now, this is at least documented, but perhaps it should be made more prominent? It seems to me that if “for i in c.indices” represents a performance pitfall then it should be regarded as an attractive nuisance.
> Nevin
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