> On 27 Jun 2016, at 04:56, Jonathan Hull via swift-evolution
> <[email protected]> wrote:
>
> Can’t a Sequence be potentially infinite, whereas a collection has a defined
> count/endIndex? Other than that, I agree with your statement.
>
> Here is what I see as the appropriate structure:
>
> Iterator: Single destructive pass, potentially infinite, (should be for-in
> able)
> Sequence: Guaranteed non-destructive multi-pass (vends Iterators),
> potentially infinite, (should be subscript-able, gain most of collection, but
> lose anything that relies on it ending)
> Collection: Multi-pass, guaranteed finite, (no changes from current form,
> except extra inits from Iterator/Sequence with end conditions)
>
> Right now we are allowed to have an infinite sequence, but calling dropLast
> or non-lazy map will cause an infinite loop. These cases could be made much
> safer by considering the potentially infinite and finite cases separately...
This seems pretty reasonable to me, though I'm not sure about subscripting
Sequence, I mean you can always add that yourself to sequence types where it
makes sense to them that way, but otherwise I think it's best to just keep it
simple and leave Sequences as a type that vends iterators over the same values.
Some methods of sequence may need to be moved to iterators though, but in
mutating form; things like .dropFirst() to skip elements, .first(where:) for
skipping to a matching element and so-on. Iterator should probably also have
the .underestimatedCount property so they can give a useful value if it can be
known.
But yeah, I think the basic structure of this makes sense, as the potentially
destructive nature of sequences doesn't seem that well known in my experience,
and I often have to go back and check my code to be sure I've avoid possible
destructive usage; I've never thought of trying to use iterators instead, might
try changing some methods and see how that goes.
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
