This is a Swift 2.0 Playground that demonstrates some use cases for lazy instantiation of object properties.

LazyInstantiation.swift

//: # Lazy Instantiation
//:
//: This playground demonstrates situations where lazily instantiating properties is valuable.
//: **NOTE:** This is a Swift 2.0 playground and must be opened in Xcode 7.

import UIKit
import CoreImage

//: A helper function to produce a random CGFloat in the range 0..<1
func randomCGFloat() -> CGFloat {
    return CGFloat(arc4random()) / CGFloat(UINT32_MAX)
}

class User : NSObject {

    /// The user's name.
    let name : String
    
    /// A greeting for the user. Cannot be used until name has been set, so it's lazy.
    lazy var greeting : String = {
        // self must be unowned or it will create a retain cycle.
        [unowned self] in
        print("Generating greeting...")
        return "Hello! My name is \(self.name)."
    }()
    
    /// A computationally intensive property. We don't want to calcualte this unless we have to!
    lazy var avatar : UIImage = {
        print ("Generating User avatar...")
        
        // Create a couple of random colors.
        let color0 = CIColor(red: randomCGFloat(), green: randomCGFloat(), blue: randomCGFloat())
        let color1 = CIColor(red: randomCGFloat(), green: randomCGFloat(), blue: randomCGFloat())
        
        // Create a CPU-driven rendering context.
        let glContext = EAGLContext(API: EAGLRenderingAPI.OpenGLES2)
        let ciContext = CIContext(EAGLContext: glContext)
        
        // Create the basic checkerboard CIImage, guarding against failure.
        guard let checkers = CIFilter(name: "CICheckerboardGenerator", withInputParameters: [
            "inputColor0" : color0,
            "inputColor1" : color1,
            kCIInputWidthKey : randomCGFloat() * 100.0 + 20.0]
            )?.outputImage else {
                // This code executes when the filter creation fails.
                print("ERROR: Unable to create checkerboard image.")
                return UIImage()
        }
        
        // Rotate the image to add some additional visual interest.
        let rotation = CGAffineTransformMakeRotation(randomCGFloat() * CGFloat(M_PI))
        let rotatedCheckers = checkers.imageByApplyingTransform(rotation)
        
        // Set up our drawing rectangle. The output size of the checkerboard is infinite, so we need to be explicit.
        let drawRect = CGRectMake(0.0, 0.0, 200.0, 200.0)
        
        // Create the output image. SWIFT BONUS: No need to manually release the returned CGImage!
        let outputImage = ciContext.createCGImage(rotatedCheckers, fromRect: drawRect)
        
        // Wrap the CGImage in a UIImage and return it.
        return UIImage(CGImage: outputImage)
    }()
    
    /// A very simple initializer.
    init(_ name: String) {
        self.name = name
    }
}

//: Create an unassuming User named "Bob".
let bob = User("Bob")

//: Accessing the property causes the creation closure to execute.
print(bob.greeting)

//: Note that  you don't see the "Generating..." message a 2nd time.
print("Second take: \(bob.greeting)")

//: Accessing the property causes the creation closure to execute. Note that the print statement inside the
//: initialization closer occurs after the greeting on the previous line, proving that it didn't execute when the
//: Object was first initialized.
//:
//: Be sure to click the (+) button in the right gutter to see the actual image.
let avatarImage = bob.avatar

//: Again, note that the "Generating..." message only happens once.
let secondCopyOfAvatar = bob.avatar