What the meaning of question mark '?' in swift?
ios, swift
Solution
You can use `if` and `let` together to work with values that might be missing. These values are represented as `optionals`. An `optional` value either contains a value or contains `nil` to indicate that the value is missing. Write a question mark (?) after the type of a value to mark the value as `optional`.
If the optional value is `nil`, the conditional is `false` and the code in braces is skipped. Otherwise, the optional value is unwrapped and assigned to the constant after `let`, which makes the unwrapped value available inside the block of code.
Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks. https://itun.es/pk/jEUH0.l
For Example:
var optionalString: String? = "Hello"
optionalString == nil
var optionalName: String? = "John Appleseed"
var greeting = "Hello!"
if let name = optionalName {
greeting = "Hello, \(name)"
}
In this code, the output would be `Hello! John Appleseed`. And if we set the value of `optionalName` as `nil`. The `if` conditional result would be `false` and code inside that `if` would get skipped.
Problem
In Swift programming I found some question marks with objects. ``` var window: UIWindow? ``` Can anybody explain the use of it?