Implement RawRepresentable on UnitMass

I'm trying to implement RawRepresentable on Measurement<UnitMass> and UnitMass in order to replace the following code with the @AppStorage decorator:

var unitOfMeasure: UnitMass {      get { AppSettings.defaults.string(forKey: "unitOfMeasure").flatMap { UnitMass.fromSymbol(rawValue: $0) }! }      set { AppSettings.defaults.set(newValue.symbol, forKey: "unitOfMeasure") }  }    var weightOverwrite: Measurement<UnitMass> {      get { .init(value: AppSettings.defaults.double(forKey: "weightOverwrite"), unit: unitOfMeasure) }      set { AppSettings.defaults.set(newValue.value, forKey: "weightOverwrite") }  }  

How can I do this? I kinda achieved it using JSONEncoder/JSONDecoder:

extension Measurement: RawRepresentable {      public init?(rawValue: String) {          guard let data = rawValue.data(using: .utf8),              let result = try? JSONDecoder().decode(Measurement.self, from: data)          else {              return nil          }          self = result      }        public var rawValue: String {          guard let data = try? JSONEncoder().encode(self),              let result = String(data: data, encoding: .utf8)          else {              return "{}"          }          return result      }  }  

But I fail to do it for UnitMass:

extension UnitMass: RawRepresentable {      public init?(rawValue: String) {          for unitMass in UnitMass.allCases where rawValue == unitLength.symbol {              self = unitLength          }                    return nil      }  }  

I get Designated initializer cannot be declared in an extension of 'UnitMass'. What am I doing wrong?

https://stackoverflow.com/questions/67238540/implement-rawrepresentable-on-unitmass April 24, 2021 at 09:26AM