How do you unwrap Swift optionals?
There are many similarities and just a handful of differences.
(Regular) Optionals
Declaration:
var opt: Type?Unsafely unwrapping:
let x = opt!.property // error if opt is nilSafely testing existence :
if opt != nil { ... someFunc(opt!) ... } // no errorSafely unwrapping via binding:
if let x = opt { ... someFunc(x) ... } // no errorSafely chaining:
var x = opt?.property // x is also Optional, by extensionSafely coalescing nil values:
var x = opt ?? nonOpt
Implicitly Unwrapped Optionals
Declaration:
var opt: Type!-
Unsafely unwrapping (implicit):
let x = opt.property // error if opt is nilUnsafely unwrapping via assignment:
let nonOpt: Type = opt // error if opt is nilUnsafely unwrapping via parameter passing:
func someFunc(nonOpt: Type) ... someFunc(opt) // error if opt is nil
Safely testing existence:
if opt != nil { ... someFunc(opt) ... } // no errorSafely chaining:
var x = opt?.property // x is also Optional, by extensionSafely coalescing nil values:
var x = opt ?? nonOpt
Since Beta 5 we have also the new coalescing operator (??):
var a : Int?
let b : Int = a ?? 0
If the optional is != nil it is unwrapped else the value on the right of the operator is used