MEDIUM: Lazy Stored Property — Swift DevTip

auto-executingClosure.swift

class SomeClass {
	lazy var fibonacciNumbers: [Int] = {
		var fibonacciNumbers = [0, 1, 1]
		for index in 2...8 {
			let currentNum = fibonacciNumbers[index]
			let prevNum = fibonacciNumbers[index - 1]
			
			let newNum = currentNum + prevNum
			fibonacciNumbers.append(newNum)
		}
		return fibonacciNumbers
	}()
	
	func addOneMoreFibonacciNumber() {
		let currentNum = fibonacciNumbers.last!
		let prevNum = fibonacciNumbers[fibonacciNumbers.count - 2]
		
		let newNum = currentNum + prevNum
		fibonacciNumbers.append(newNum)
	}
}

let instance = SomeClass()
instance.addOneMoreFibonacciNumber()

methodImplementation.swift

class SomeClass {
	lazy var fibonacciNumbers = self.createFirstFewFibonacciNumbers()
	
	func addOneMoreFibonacciNumber() {
		let currentNum = fibonacciNumbers.last!
		let prevNum = fibonacciNumbers[fibonacciNumbers.count - 2]
		
		let newNum = currentNum + prevNum
		fibonacciNumbers.append(newNum)
	}
	
	private func createFirstFewFibonacciNumbers() -> [Int] {
		var fibonacciNumbers = [0, 1, 1]
		for index in 2...8 {
			let currentNum = fibonacciNumbers[index]
			let prevNum = fibonacciNumbers[index - 1]
			
			let newNum = currentNum + prevNum
			fibonacciNumbers.append(newNum)
		}
		return fibonacciNumbers
	}
}

let instance = SomeClass()
instance.addOneMoreFibonacciNumber()

simpleLazyProperty.swift

class SomeClass {
	lazy var storedProp = ""
}

let instance = SomeClass()
instance.storedProp // The property isn't initialized until this point