Set (Collection) - Insert multiple elements

Question

Set is an unordered collection of unique elements. Almost similar to array.

I want to add/insert multiple elements in a Set of String. But there is only single method provided that can insert only one element (accepts single Set element as a parameter argument) and I've collection of string (id).

insert(_:)

@discardableResult mutating func insert(_ newMember: Set.Element) -> (inserted: Bool, memberAfterInsert: Set.Element)

How can I do that?

What I've tried:
I tried to create an extension very similar to insert(_:) method but it can accept multiple Set elements. It would be same as use of iteration over collection but don't need to handle it manually everywhere.

extension Set {

    @discardableResult mutating func insert(_ newMembers: [Set.Element]) -> (inserted: Bool, memberAfterInsert: Set.Element) {

        newMembers.forEach { (member) in
            self.insert(member)
        }
    }
}

It should work, if I return a tuple as expected but no idea how and where (which line) and what to return a value.

Here is error message.

Missing return in a function expected to return '(inserted: Bool, memberAfterInsert: Set.Element)'

What can be solution to this. Is there any better solution/approach to handle this operation?

Answer 1

It was pointed out in the comments under the question, but I'd like to clearly state that there is a method for that very same purpose:

mutating func formUnion<S>(_ other: S) where Element == S.Element, S : Sequence

Usage:

var attendees: Set = ["Alicia", "Bethany", "Diana"]
let visitors = ["Diana", "Marcia", "Nathaniel"]
attendees.formUnion(visitors)
print(attendees)
// Prints "["Diana", "Nathaniel", "Bethany", "Alicia", "Marcia"]"

Source: Apple Developer

---

There is also an immutable variant which returns a new instance containing the union:

func union<S>(_ other: S) -> Set<Set.Element> where Element == S.Element, S : Sequence

Usage:

let attendees: Set = ["Alicia", "Bethany", "Diana"]
let visitors = ["Marcia", "Nathaniel"]
let attendeesAndVisitors = attendees.union(visitors)
print(attendeesAndVisitors)
// Prints "["Diana", "Nathaniel", "Bethany", "Alicia", "Marcia"]"

Source: Apple Developer