Associated Values

enum NetworkResult {
    case success(code: Int)
    case failure(message: String)
}
let result = NetworkResult.success(code: 200)
switch result {
case .success(let code):
    print("Success with code \(code)")
case .failure(let message):
    print("Failed: \(message)")
}

enum Shape {
    case circle(radius: Double)
    case rectangle(width: Double, height: Double)
}
let shapes = [Shape.circle(radius: 3), Shape.rectangle(width: 4, height: 5)]
for shape in shapes {
    switch shape {
    case .circle(let radius):
        print("Circle with radius \(radius)")
    case .rectangle(let width, let height):
        print("Rectangle \(width) x \(height)")
    }
}

1. Confusing associated values (data attached per-instance, extracted via pattern matching) with raw values (a single fixed value per case, retrieved via .rawValue).
2. Forgetting you must use switch or if case with let/var bindings to extract associated values -- you can't access them like a normal property.
3. Trying to give an enum both raw values and associated values on the same cases; Swift doesn't allow mixing the two on one enum.

• Associated values let each case carry its own extra data of specified types.
• Extracting associated values requires pattern matching, typically with switch or if case.
• Different cases in the same enum can carry entirely different associated data.
• Associated values make enums powerful for modeling variant data, like network results.