DependencyInjection.swift

import Foundation

// Dependency Injection

/*
 Dependency Injection is often used with the intention of writing code that is loosely coupled, and thus, easier to test.
 
 Types of dependecy injection:
  1. Property Injection
  2. Constructor Injection
  3. Interface Injection
 */

// 1. Property Injection
struct Profession {
    var name : String
}

// This involves tight coupling and creating it's own dependency
struct George {
    var profession = Profession(name: "Engineer") // This is tight coupling
    var subProfession : Profession?
}
var user = George()
user.subProfession = Profession(name: "Tester") // This is property injection


//2.  Constructor Injection
struct Tony {
    var profession : Profession

    init(_ profession: Profession) {
        self.profession = profession
    }
}
let tony = Tony(Profession(name: "Doctor"))

//3. Interface Injection
protocol Dependency {}

protocol HasDependency {
    func setDependency(_ dependency: Dependency)
}

protocol DoesSomething {
    func doSomething()
}

class Client: HasDependency, DoesSomething {
    private var dependency: Dependency!
    
    func setDependency(_ dependency: Dependency) {
        self.dependency = dependency
    }
    
    func doSomething() {
        // Does something with a dependency
    }
}