[swift-users] Why does RangeReplaceableCollection require an empty initialiser?

Zach Waldowski zach at waldowski.me
Wed Jul 6 15:21:35 CDT 2016

I have the same misgivings. The other day, I was wanted to add a piece
of metadata to a Slice type conforming to RangeReplaceableCollection
(coming from the containing collection) but couldn't figure out a way to
make it safe with the empty initializer. It's bugged me a few times

  Zachary Waldowski
  zach at waldowski.me

On Wed, Jul 6, 2016, at 04:09 AM, Tim Vermeulen via swift-users wrote:
> RangeReplaceableCollection has three initialisers: init(), init(_:) and
> init(repeating:count:). The latter two are implemented using the empty
> initialiser. But why are these initialisers part of this particular
> protocol? As far as I can tell, no other methods of this protocol depend
> on these initialisers. The requirement of the empty initialiser makes it
> impossible to have a collection conform to this protocol that needs
> additional data for its initialisation.
> For instance, I was making an array that works with any Strideable
> indices, not just integers. A startIndex is needed for its
> initialisation, so I can’t really conform it to
> RangeReplaceableCollection. If I do it anyways (with a fatalError() in
> the required empty initialiser) everything seems to work just fine,
> except for the protocol’s three initialisers.
> Perhaps these initialisers should be moved to a (possible new) different
> protocol?
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