[swift-evolution] Passing an optional first argument to sequence(first:next:)

[Pyry Jahkola]

> Max Moiseev wrote:
> 
> FWIW, the ‘classical’ way of doing what I think you’re trying to do is:
> 
> extension Sequence {
>  var pairs: AnySequence<(Iterator.Element, Iterator.Element)> {
>    return AnySequence(zip(self, self.dropFirst()))
>  }
> }
> 
> Does it have the right behavior?

It doesn't if the sequence is single-pass or if iterating over it multiple times has other unwanted side-effects.

— Pyry