If you want to match [UInt8] specifically, just use the non-sugared definition:
extension RawBits where RawValue == Array<UInt8> {
}
If you want it to match any array, that’s more complicated. As far as I’ve been
able to work out, you have to wrap it in a protocol. Most of Array’s usefulness
comes from protocols anyway, so you can probably use Sequence, Collection, or
one or more of the more specific
Mutable/RandomAccess/RangeReplaceableCollection protocols.
extension RawBits where RawValue: Collection {
}
If you really need an array specifically, as far as I can tell you have to use
a pattern I’ve used for a similar purpose with optionals:
protocol Arrayable {
associatedtype T
func asArray() -> [T]
}
extension Array: Arrayable {
func asArray() -> [Element] {
return self
}
}
extension RawBits where RawValue: Arrayable {
func foo() {
let ary = rawValue.asArray()
// ary is now an Array.
}
}
It’s rather unfortunate this requires a somewhat ugly workaround, but, well,
it’s not the worst or most commonly encountered of the shortcomings in the type
system.
> On Dec 13, 2017, at 9:42 PM, Frank Swarbrick via swift-users
> <swift-users@swift.org> wrote:
>
> I have the following:
>
> public protocol RawBits: CustomStringConvertible, Collection {
> associatedtype RawValue
> var rawValue: RawValue { get set }
> }
>
> extension RawBits where RawValue: FixedWidthInteger, RawValue:
> UnsignedInteger {
> [...fields and methods are defined here...]
> }
>
> struct RawBits8: RawBits {
> var rawValue: UInt8
> }
>
> This all works fine.
> Now I want to be able to define an extension to which the following would
> conform:
>
> struct RawBitsX: RawBits {
> var rawValue: [UInt8]
> }
>
> rawValue is now an array rather than a simple type. I can't for the life of
> me figure out how to indicate this in the 'where' clause of an extension to
> RawBits. Can this be done? How?
>
> Thanks for any assistance,
> Frank
> _______________________________________________
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> swift-users@swift.org <mailto:swift-users@swift.org>
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