Confused (and a little frustrated) with Swift5 at the moment.

I have a method:

func oidsMany(_ oids:Array<UInt32>) -> MCCommandBuilder {
    let sorted_oids:[UInt32] = oids.sorted()
    ...
}

Discovered I have a case where I want to pass a Set to this method just as well. Either way, I'm going to sort an Array or a Set to an Array right away.

Waded through the many many many protocols that both Set and Array conform to, noticed that they both conform to [Sequence][1] and that Sequence responds to sorted. Perfect.

But when I change the above to:

func oidsMany(_ Sequence<UInt32>) -> MCCommandBuilder {
    let sorted_oids:[UInt32] = oids.sorted()
    ...
}

I get the following error hints:

Cannot specialize non-generic type 'Sequence'
Member 'sorted' cannot be used on value of protocol type 'Sequence'; use a generic constraint instead

What's the right way to approach this? I could just add a second oidsMany(_ Set...) that casts its arg as an array and recalls. But I feel like I'm missing something fundamental here. My experience from other languages is not mapping over well here.

CodePudding user response：

You can as the error message suggest use it as a generic constraint instead

func oidsMany2<Sortable: Sequence>(_ oids: Sortable) -> MCCommandBuilder where Sortable.Element: Comparable {
    let sorted_oids:[Sortable.Element] = oids.sorted()
    //...
}

if you only want to accept collections where the element is UInt32 you can change the where condition to

where Sortable.Element == UInt32