[swift-evolution] [Proposal]: Drastically improve searching API (indexOf(…)) of CollectionType

[Brent Royal-Gordon]

I'm not sure about the rest of this, but...

>> 1. A backwards-compatible refactoring of `CollectionType.indices`, moving it to `Indexable`.
>> 
>> 2. A backwards-compatible refactoring of `indexOf(…)` (adding optional `range:` and moving it to `Indexable`).
>> 
>> 3. The addition of `rangeOf(…)`, `countOf(…)` and `isSorted(…)` to `Indexable` with a TIME complexity of `O(self.count)`.
>> 
>> 4. The introduction of a `BinarySearchView` on `Indexable`, allowing for fast (`O(log2(self.count))`) searches on `Indexable` via `indexOf(…)`, `rangeOf(…)`, `countOf(…)`, `lowerBoundOf(…)`, `upperBoundOf(…)` without cluttering `Indexable`'s interface.

I don't think you quite understand what `Indexable` is for.

`Indexable` is a minimal protocol containing the very most basic parts of `CollectionType`'s interface. It's used to avoid circular definitions in `CollectionType`. The doc comments on it describe it as "almost an implementation detail". I don't think it's appropriate to move a whole bunch of stuff into `Indexable` when it's supposed to be a minimal protocol.

-- 
Brent Royal-Gordon
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