some and any keywords for generic protocols in Swift 5.7

someAndAnyOnSwift5_7.swift

/*
 some and any keywords for generic protocols in Swift 5.7
 https://swiftbysundell.com/articles/referencing-generic-protocols-with-some-and-any-keywords/
 */

protocol Item { }
struct User {
    let name: String
    var isAnonymous: Bool {
        return name.isEmpty
    }
}
protocol Group {
    associatedtype Item
    
    var items: [Item] { get }
    var users: [User] { get }
}

/*
 Runtime Error:
 required by global function 'namesOfUsers(addedTo:)' where 'some Group' = 'any Group'
 
 As I use namesOfUsers in showDepartment with `some Collection<any Group>` typed groups,
 The below error happens at `print(namesOfUsers(addedTo: group))`.
 
 error: type 'any Group' cannot conform to 'Group'
 only concrete types such as structs, enums and classes can conform to protocols
 */
//func namesOfUsers(addedTo group: some Group) -> [String] {

func namesOfUsers(addedTo group: any Group) -> [String] {
    group.users.compactMap { user in
        user.isAnonymous ? nil : user.name
    }
}

struct Devs: Group {
    typealias Item = Int
 
    let items: [Int]
    let users: [User]
}

let devs = Devs(items: [1,2,3,4,5],
                users: ["", "bob", "john", "", "kate"].map(User.init))
print(namesOfUsers(addedTo: devs))
// ["bob", "john", "kate"]

// Here's another group.
struct Designers: Group {
    typealias Item = String
    
    let items: [String]
    let users: [User]
}

let designers = Designers(items: ["graphics", "navigation", "architecture", "requirements"],
                          users: ["", "elen", "steve", ""].map(User.init))

func showDepartment(consistsOf groups: some Collection<any Group>) {
    groups.forEach { group in
        print(group.items)
        print(namesOfUsers(addedTo: group))
    }
}
let groups: [any Group] = [devs, designers]
showDepartment(consistsOf: groups)
/*
 [1, 2, 3, 4, 5]
 ["bob", "john", "kate"]
 ["graphics", "navigation", "architecture", "requirements"]
 ["elen", "steve"]
 */