Protocol dispatching

prot_disp.swift

// MARK: - Protocol definitions
protocol InputProtocol {
  var a: Int { get }
  var b: Int { get }
}

protocol Addition: InputProtocol {}
extension Addition {
  func operation() -> Int{
    return a + b
  }
}

protocol Subtraction: InputProtocol {}
extension Subtraction {
  func operation() -> Int{
    return a - b
  }
}

protocol Multiplication: InputProtocol {}
extension Multiplication {
  func operation() -> Int{
    return a * b
  }
}

// MARK: - Struct and typealias definitions
typealias Operations = Addition & Subtraction & Multiplication

struct Calculator: Operations {
  var a: Int
  var b: Int
  
  //Default operation
  func operation() -> Int{
    return 0
  }
}

// MARK: - Implementation
let calculation = Calculator(a: 5, b: 3)

let add: Addition = calculation
add.operation()  // prints 8

let sub: Subtraction = calculation
sub.operation()  // prints 2

let mult: Multiplication = calculation
mult.operation() // prints 15