Using Optional Binding

Swift Programming: The Big Nerd Ranch Guide (2nd E 8. Optionals
1

Hi,
I am currently reading “The Nil Coalescing Operator”. There is a program as below:

import UIKit

var errorCodeString : String?
errorCodeString = “404”
var errorDescription : String?

if let theError = errorCodeString, let errorCodeInteger = Int(theError), errorCodeInteger == 404 {

errorDescription = "\(errorCodeInteger + 200) : resource was not found."

}

var upCaseErrorDescription = errorDescription?.uppercased ()
errorDescription

upCaseErrorDescription?.append(“PLEASE TRY AGAIN”)
upCaseErrorDescription

errorDescription = nil
let description: String
if let errorDescription = errorDescription {
description = errorDescription
} else {
description = “NO ERROR”
}

For this line:
if let errorDescription = errorDescription
errorDescription has been declared as variable since the beginning and declared again as constant here. I am confused here. Are these two “errorDescription” the same?
Appreciate your help. Thank you.

2

No the constant lives only in the if scope. It is quite confusing at first… I know!

3

How do you get the value of an optional out of an if loop? For example if the optional has a value and you unwrap this in the loop, how can you then get the value out of the loop to use later in your program?

4

You can use guard statement like:
guard let unwrappedOptional = optional else { continue or break or return }
// from now on you can use unwrappedOptional

5

Another solution:

let unwrappedOptional = optional ?? defaultValue

// from now on you can use unwrappedOptional