Retroactive Modelling in Swift

Protocol Extensions and Protocol Oriented Programming Techniques

• Extension add new functionality to an existing class, structure, enumeration, or protocol type

Extension in Swift can: - Add computed instance propterties and computed type properties - Define instance methods and type methods - Provide new initializer - Define subscripts - Define and use new nested types - Make an existing type conform to a protocol

Example extending the type of Double

extension Double {
  // Meters
  var m: Double { return self }
  
  // Millimeters
  var mm: Double { return self / 1000 }

  func descriptionInMeters() -> String {
    return "\(self)m"
  }

  // Mutating function: Value type of Struct
  mutating func resetToZero() {
    self = 0.0
  }
}

var oneInch = 25.4.mm
var description = 2.3.descriptionInMeters()

value = 2.0
value.resetToZero()