[swift-users] error: value of type 'Self.SubSequence' has no member 'Distance'

[Dmitri Gribenko]

On Wed, Dec 23, 2015 at 3:24 PM, Daniel Eggert via swift-users
<swift-users at swift.org> wrote:
> I have an array of String and need to call withCString on each one and then pass the resulting array of UnsafePointer<Int8> to a C api. The unsafe pointer is only valid within the scope of withCString.
>
> So I built the following, but the compiler doesn’t like it:
>
> % swift scopedReduceAndApply.swift
> scopedReduceAndApply.swift:18:16: error: value of type 'Self.SubSequence' has no member 'Distance'
>         return tail.scopedReduceAndApply(f, g: g, list: ll)
>                ^~~~ ~~~~~~~~~~~~~~~~~~~~
>
> What is ‘Distance’ and why doesn’t SubSequence of CollectionType have it?

That's just a bad error message.

> extension CollectionType where SubSequence : CollectionType {

I think you need this constraint to be propagated all the way down,
for recursive calls, so you need:

extension CollectionType where SubSequence == Self

Or, if you want to allow the toplevel type to differ:

extension CollectionType
  where
  SubSequence : CollectionType,
  SubSequence.SubSequence == SubSequence

Dmitri

-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/