[swift-evolution] [Review] SE-0045: Add scan, prefix(while:), drop(while:), and iterate to the stdlib

[Brent Royal-Gordon]

> The proposal has been updated as per feedback from the core team (https://github.com/apple/swift-evolution/pull/275). This includes removing some last vestiges of Swift 2 naming as well as replacing `iterate(_:apply:)` with an overloaded function `unfold(_:applying:)`.

The proposal says this:

	public func unfold<T, State>(_ initialState: State, applying: State -> (T, State)?) -> UnfoldSequence<T>
	public func unfold<T>(_ initialElement: T, apply: T -> T) -> UnfoldSequence<T>

However, the comment implies that the second one should instead be this:

	public func unfold<T>(_ initialElement: T, applying: T -> T?) -> UnfoldSequence<T>

I'm not sure I like having these be overloaded on only the return type of the closure. Maybe we could do something like this?

	public func unfold<T, State>(fromState initialState: State, applying: State -> (T, State)?) -> UnfoldSequence<T>
	public func unfold<T>(fromFirst initialElement: T, apply: T -> T) -> UnfoldSequence<T>

That way you're calling either `unfold(fromState:applying:)` or `unfold(fromFirst:applying:)`. (Some further bikeshedding might be needed here—it's late and I'm tired.)

-- 
Brent Royal-Gordon
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