[swift-evolution] zip3, zip4, ...

[Erica Sadun]

It's pretty easy to build your own Zips. Not sure the language really needs this. For example, I recently built a zip that produces (T?, T?) which fills one of the two with nil until both lists are consumed:

func longZip<S0: SequenceType, S1: SequenceType>(seq0: S0, _ seq1: S1) ->
    AnyGenerator<(S0.Generator.Element?, S1.Generator.Element?)> {
        var generators = (seq0.generate(), seq1.generate())
        return anyGenerator {
            let items = (generators.0.next(), generators.1.next())
            if case (.None, .None) = items {return nil}
            return items
        }
}

I'm rather fond of this variant although I don't know if it's generally useful enough to be worth even considering for the language

-- E


> On Dec 6, 2015, at 4:01 PM, Jacob Bandes-Storch via swift-evolution <swift-evolution at swift.org> wrote:
> 
> zip2 (aka "zip") is present in Swift. zip3 is often useful, but not built-in.
> 
> It can be achieved by using multiple copies of zip2:
> 
>   for (one, (two, three)) in zip(list1, zip(list2, list3)) ...
> 
> It seems like either of these could make sense:
> 
> - Put some reasonable number of implementations, like zip2...zip10, in the standard library, using gyb.
> 
> - Have the compiler generate them on the fly as requested by the user.
> 
> Or, some alternate approaches:
> 
> - Don't do this right now, but count it as motivation for a macro system.
> 
> - Consider making Swift's pattern-matching system extensible, which might allow custom array-based patterns, like "for [one, two, three] in zip(list1, list2, list3)".  (I've been thinking of writing a proposal for this anyway.)
> 
> 
> Does anyone else care about zip3-and-higher? How do these options sound?
> 
> Jacob Bandes-Storch
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