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

[Zhao Xin]

N
​o. You didn't catch what I meant. I meant it should be like an equation.
​If foo is a
​RangeReplaceableCollection,
​
foo
 minus
foo
 equates zero, zero means an empty collection. Both side of the equation
should be with the same unit, the unit is
RangeReplaceableCollection.
​ Below code also shows init() is useful in
RangeReplaceableCollection.
​​

var foo = Array<Int>()
>
> foo.append(contentsOf: [2,4,6,8])
>

​Zhaoxin

On Wed, Jul 6, 2016 at 10:07 PM, Tim Vermeulen <tvermeulen at me.com> wrote:

> You wouldn’t need an empty initialiser to remove all elements from a
> collection, right? You could just use `replaceRange` instead.
>
> > Now I understood you concerns. Have you ever thought of if a non-empty
> RangeReplaceableCollection being removed all of its elements, which makes
> the collection to be an empty collection. That shouldn't change
> theRangeReplaceableCollection to be a non-RangeReplaceableCollection. Sothe
> empty collection must also be aRangeReplaceableCollection.
> >
> > > init()
> >
> (file:///Users/zhaoxin/Library/Application%20Support/Dash/DocSets/Apple_API_Reference/Apple_API_Reference.docset/Contents/Resources/Documents/
> developer.apple.com/reference/swift/rangereplaceablecollection/1641467-init.html)>
> Creates a new, empty collection.
> >
> > Zhaoxin
> >
> > On Wed, Jul 6, 2016 at 9:09 PM, Tim Vermeulen<tvermeulen at me.com(mailto:
> tvermeulen at me.com)>wrote:
> > > I’m not allowing generic subscripts. The collection is declared as
> `AnyIndexArray<Index: Strideable, Element where Index.Stride == Int>` and
> it can be subscripted with type `Index`.
> > >
> > > Either way, it’s not really important. I’m mostly wondering why
> RangeReplaceableCollection needs an empty initialiser.
> > >
> > > >Then how you defined the index to conform toStrideable? Below code
> does work as it seams that you can't use generics in subscripts.
> > > >
> > > >
> > > >subscript<T:Strideable>(index:T) ->Element
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >Zhaoxin
> > > >
> > > >
> > > >
> > > >
> > > >On Wed, Jul 6, 2016 at 8:32 PM, Tim Vermeulen<tvermeulen at me.com
> (mailto:tvermeulen at me.com)(mailto:tvermeulen at me.com)>wrote:
> > > >>
> > > >>>On 6 Jul 2016, at 14:03, Zhao Xin<owenzx at gmail.com(mailto:
> owenzx at gmail.com)(mailto:owenzx at gmail.com)>wrote:
> > > >>>According to the document of Swift 3, Array has already conformed
> protocolRangeReplaceableCollection.
> > > >>
> > > >>That’s exactly why I also want to conform my wrapper to that
> protocol? I think there’s a misunderstanding. I’m making a collection that
> can be subscripted with any index (that conforms to Strideable), but
> behaves like an array otherwise.
> > > >>
> > > >>>
> > > >>>Zhaoxin
> > > >>>
> > > >>>On Wed, Jul 6, 2016 at 7:09 PM, Tim Vermeulen via swift-users<
> swift-users at swift.org(mailto:swift-users at swift.org)(mailto:
> swift-users at swift.org)>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?
> > > >>>>_______________________________________________
> > > >>>>swift-users mailing list
> > > >>>>swift-users at swift.org(mailto:swift-users at swift.org)(mailto:
> swift-users at swift.org)
> > > >>>>https://lists.swift.org/mailman/listinfo/swift-users
> > > >>>
> > > >>
> > > >
> > > >
> > > >
> >
> >
> >
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