Enum with raw type cannot have cases with arguments
Swift enum can have either raw values or associated values, but not both at the same time. In your case, case max = 1 is a raw value, while custom(CGFloat) is an associated value.
To overcome this limit, you could use an enum with associated values with a computed property:
enum JPEGCompressionLevel { case custom(CGFloat) case max, high, med, low var value: CGFloat { switch self { case .max: return 1.0 case .high: return 0.9 case .med: return 0.5 case .low: return 0.2 case .custom(let customValue): return customValue } }}let a: JPEGCompressionLevel = .custom(0.3)let b: JPEGCompressionLevel = .maxprint(a.value)print(b.value)For more information, you can refer to this article.