Swift : Enum case not found in type

Question

I have been searching for many questions here, I found one with similar title Enum case switch not found in type , but no solution for me.

I'd like to use enum with mutation of itself to solve question, what is the next traffic light color, at individual states.

enum TrafficLights {
    mutating func next() {
        switch self {
        case .red:
            self = .green
        case .orange:
            self = .red
        case .green:
            self = .orange
        case .none:
            self = .orange
        }
    }
}

I have put all cases as possible options and it's still returning error:

Enum 'case' not found in type 'TrafficLights'

Answer 1

I was having an issue with the same error when converting an Int to a custom enum:

switch MyEnum(rawValue: 42) {
case .error:
    // Enum case `.error` not found in type 'MyEnum?'
    break
default:
    break
}

The issue is that MyEnum(rawValue: 42) returns an optional. Unwrap it or provide a non-optional to allow switching on the enum:

switch MyEnum(rawValue: 42) ?? MyEnum.yourEnumDefaultCase {
case .error:
    // no error!
    break
default:
    break
}

Answer 2

The cases must be declared outside of the function:

enum TrafficLights {

case green
case red
case orange
case none

mutating func next() {
    switch self {
    case .red:
        self = .green
    case .orange:
        self = .red
    case .green:
        self = .orange
    case .none:
        self = .orange
    }
  }
}

Advisable:- Go through Enumeration - Apple Documentation