fibonacci.swift

class Fibonacci {
    var value: Int
    
    init(value: Int) {
        self.value = value
    }
    
    lazy var fibonacci: () -> Int = { [unowned self] in
        // Some temporary variables.
        var a = 0
        var b = 1
        
        // Add up numbers to the desired iteration.
        for _ in 0..<self.value {
            let temp = a
            a = b
            b = temp + b
        }
        
        return a
    }
    
    deinit {
        print("\(value) is being deinitialized. Memory deallocated")
    }
}

let f = Fibonacci(value: 7)
f.fibonacci()

//var t: Fibonacci? = Fibonacci(value: 8)
//t?.fibonacci()
//t = nil