protocol EnumProtocol {
    static var startValue: Self { get }
    func nextValue() -> Self
}

enum FooState: EnumProtocol {
    case foo1, foo2
    static var startValue: FooState { return .foo1 }
    func nextValue() -> FooState {
        switch self {
        case .foo1:
            return .foo2
        case .foo2:
            return .foo1
        }
    }
}

enum BarState: EnumProtocol {
    case bar
    static var startValue: BarState { return .bar }
    func nextValue() -> BarState {
        return .bar
    }
}


class BaseClass<T: EnumProtocol> {
    var state = T.startValue
}

class FooClass: BaseClass<FooState> {
}

class BarClass: BaseClass<BarState> {
}

let foo = FooClass()
let bar = BarClass()
if let test = bar as? BaseClass {
    test.state = test.state.nextValue()
}

let bar = BarClass()
if let test = bar as? BaseClass<BarState> {
    test.state = test.state.nextValue()
}

error: generic parameter 'T' could not be inferred in cast to 'Wallet<_>'