Hi Rick,
I think you’re looking for something like this? Assuming when you say “return”
in your bullet spec you mean assign-in-place since we’re talking about +=
func +=<T>(lhs: inout [T]?, rhs: [T]?) {
switch (lhs,rhs) {
case (_,nil): return // no-op whether lhs is
nil or not when rhs is
case (nil,_?): lhs = rhs // lhs of nil gets replaced
case (_?,let rhs?): lhs!.append(contentsOf: rhs) // neither nil: append
in-place
}
}
(you could make rhs generic over sequences too but then you don’t get automatic
handling of subclasses of T on the rhs)
But it’s probably not a good idea to overload += like this since the extra
handling of nils, especially on the lhs, is a bit out of the expected behavior
for += and could backfire if you accidentally used it somewhere you didn’t
expect. So maybe make it a method with a new name, like:
extension Optional where Wrapped: RangeReplaceableCollection {
mutating func maybeAppend(others: [Wrapped.Iterator.Element]?) {
switch (self,others) {
case (_,nil): return
case (nil,let x?): self = Wrapped(x)
case (_?,let x?): self!.append(contentsOf: x)
}
}
}
> On Oct 20, 2016, at 5:17 PM, Rick Mann via swift-users
> <swift-users@swift.org> wrote:
>
> When working with URLComponents query items, it would be nice to write code
> like this:
>
> var oqi: [URLQueryItem]? = [..., ..., ...]
>
> var comps = URLComponents(…)
> comps.queryItems += oqi
>
> The problem is that queryItems is [URLQueryItem]?, and so I can't just
> append. I'd like to write a version of += that:
>
> • Takes an LHS of [URLQueryItems]?, RHS of [things possibly derived from
> URLQueryItem]?
> • if LHS != nil, make an array of LHS, and optionally append RHS, and return
> that
> • if LHS == nil && RHS != nil, return RHS
> • If both are nil, return nil
>
> I'd like to do this in a generic way that works for any type on the left and
> possibly-dervied types on the right.
>
> --
> Rick Mann
> rm...@latencyzero.com
>
>
> _______________________________________________
> swift-users mailing list
> swift-users@swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
_______________________________________________
swift-users mailing list
swift-users@swift.org
https://lists.swift.org/mailman/listinfo/swift-users
