protocol GroupMember: Role {
    var groupNumber: Int {set get}
}
protocol GroupAdmin: GroupMember { }

struct BrowseGroup: Action {
    let group: Group
    
    init() {  // required default initializer
        group = Group(groupNumber: -1, isPublicGroup: false) // default froup
    }
    
    init(group: Group) {
        self.group = group
    }
}

class GroupAdminUser: User, GroupAdmin {
    var groupNumber: Int
    init(name: String, age: Int, groupNumber: Int) {
        self.groupNumber = groupNumber
        super.init(name: name, age: age)
    }
    
    override required init() {
        self.groupNumber = -1
        super.init()
    }
}

GroupMemberUser.shouldBeAbleTo(BrowseGroup.action).when {
    guard let groupMember = $0 as? GroupMember,
        let browseAction = $1 as? BrowseGroup else { return false }
    return groupMember.groupNumber == browseAction.group.groupNumber
}
GroupAdminUser.shouldBeAbleTo(DeleteGroup.action).when {
    guard let groupAdmin = $0 as? GroupAdminUser,
        let deleteAction = $1 as? DeleteGroup else {
            return false
    }
    return groupAdmin.groupNumber == deleteAction.group.groupNumber
}
_ = SuperAdminUser.shouldBeAbleTo(BrowseGroup.action)

let member1 = GroupMemberUser(name: "member1", age: 18, groupNumber: 1)
let admin2 = GroupAdminUser(name: "admin2", age: 22, groupNumber: 2)
let group1 = Group(groupNumber: 1, isPublicGroup: false)
let group2 = Group(groupNumber: 2, isPublicGroup: false)
member1.can(BrowseGroup(group: group1) // true
member1.can(BrowseGroup(group: group2) // false
admin2.can(BrowseGroup(group: group1) // true: GroupAdmin inherits BrowseGroup permission from GroupMember
admin2.can(DeleteGroup(group: group2) // true
admin2.can(DeleteGroup(group: group1) // false