ProtocolImmutableError.swift

protocol Expandable {
    var isExpanded: Bool { get set }
}

class Bag: Expandable {
    var isExpanded = true
}

class CarryOn: Expandable {
    var isExpanded = true
}

class Closet: Expandable {
    var isExpanded = true
}

let bag = Bag()
let carryOn = CarryOn()
let closet = Closet()
let expandableItems: [Expandable] = [bag, carryOn, closet]
// expandableItems.forEach { $0.isExpanded = false } // Here !!! I got an immutable error