Intermediate Swift Tutorial on RayWenderlich.com: Solution to Exercise in Part 9: Memory Managment

MemoryManagementPlayground.swift

// Part 09: Memory Management
// Swift 2.0 (Xcode 7 Beta 1)
// "Uber" Challenge Exercise from Ray Wenderlich's "Intermediate Swift Series", Part 9.
// Series available here: http://www.raywenderlich.com/video-tutorials#swift 
// Solution created by Sohail Ahmed, twitter: @idStar, blog: http://sohail.io

class Conference {
    var name:String
    var instructors:[Instructor] = Array<Instructor>()
    var students:[Student] = Array<Student>()
    var sessions:[Session] = Array<Session>()
    
    init(name: String) {
        self.name = name
    }
    
    deinit {
        print("Conference de-initialized: \(name)")
        instructors.removeAll()
        students.removeAll()
        sessions.removeAll()
    }
}


class Instructor {
    var name:String = ""
    weak var session:Session?
    
    init(name:String, session: Session) {
        self.name = name
        self.session = session
    }
    
    deinit {
        print("Instructor de-initialized: \(name)")
        session = nil
    }
}


class Session {
    var name:String = ""
    weak var instructor:Instructor?
    var students:[Enrollment] = Array<Enrollment>()
    
    init(name: String, instructor:Instructor?) {
        self.name = name
        self.instructor = instructor
    }
    
    convenience init(name: String) {
        self.init(name: name, instructor: nil)
    }
    
    deinit {
        print("Session de-initialized: \(name)")
        instructor = nil
        students.removeAll()
    }
}


class Student {
    var firstName:String = ""
    var lastName:String = ""
    var sessions:[Enrollment] = Array<Enrollment>()

    init(firstName:String, lastName:String) {
        self.firstName = firstName
        self.lastName = lastName
    }
    
    deinit {
        print("Student de-initialized: \(firstName) \(lastName)")
        sessions.removeAll()
    }
}


struct Enrollment {
    weak var student:Student?
    weak var session:Session?
    
    init(student:Student, session:Session) {
        self.student = student
        self.session = session
        
        self.student?.sessions.append(self)
        self.session?.students.append(self)
    }
}


// Conference
var rwDevCon:Conference? = Conference(name:"RW Dev Con")

// Sessions
var spriteKitSession:Session? = Session(name: "Introduction to Sprite Kit")
var adaptiveLayoutSession:Session? = Session(name: "Using Adaptive Layout")
var watchKitSession:Session? = Session(name: "Introducing WatchKit")
rwDevCon?.sessions = [spriteKitSession!, adaptiveLayoutSession!, watchKitSession!]

// Instructors
var ray:Instructor?  = Instructor(name: "Ray Wenderlich", session: spriteKitSession!)
var greg:Instructor? = Instructor(name: "Greg Heo", session: adaptiveLayoutSession!)
var mic:Instructor?  = Instructor(name: "Mic Pringle", session: watchKitSession!)
rwDevCon?.instructors = [ray!, greg!, mic!]

// Students
var student1:Student? = Student(firstName: "Reinhold", lastName: "Messner")
var student2:Student? = Student(firstName: "Gerlinde", lastName: "Kaltenbrunner")
var student3:Student? = Student(firstName: "Jrezy", lastName: "Kukuczka")
var student4:Student? = Student(firstName: "Ed", lastName: "Viesturs")
rwDevCon?.students = [student1!, student2!, student3!, student4!]

// Assigning Students to Sessions:
Enrollment(student: student1!, session: spriteKitSession!)
Enrollment(student: student1!, session: watchKitSession!)
Enrollment(student: student2!, session: adaptiveLayoutSession!)
Enrollment(student: student3!, session: watchKitSession!)
Enrollment(student: student4!, session: watchKitSession!)

// Next, we'll set our local, optional variables to nil, so we can see that they
// actually get released from the Conference object graph when our conference, rwDevCon,
// is finally released.

// Remove: Sessions
spriteKitSession = nil
adaptiveLayoutSession = nil
watchKitSession = nil

// Remove: Instructors
ray = nil
greg = nil
mic = nil

// Remove: Students
student1 = nil
student2 = nil
student3 = nil
student4 = nil

// Only once we set the following to nil, do we see the cascade of de-initializers
// from the object graph that it contains. Comment this line out to see the change:
rwDevCon = nil