When you assign data to a variable, that data defines the data type. But "nil" does not have a data type. Therefore Swift will throw an error.
Every time you create a variable, you must define its type, whether by explicitly defining it
var name: String
var age: Int
or by entering data in it
var name = "Sedat"
var age = 44
But if you neither not define the type nor do not enter data into a variable, swift cannot know the type of the variable.
var name // Error: Type annotation missing in pattern
var age // Error: Type annotation missing in pattern
Sometimes you may not want to define its type in advance. In such a situation, it will be empty. So entering "nil" does not solve the problem because it does not have any data type.
var name = nil // Error: 'nil' requires a contextual type
var age = nil // Error: 'nil' requires a contextual type
And sometimes you can define the data type but you don't exactly know which type is it, in such a situation you may think adding a "nil" may solve it, but it does not
var name: String = nil // Error: 'nil' cannot initialize specified type 'String'
var age: Int = nil // Error: 'nil' cannot initialize specified type 'String'
But adding an optional sign "?" to the type may solve the problem
var name: String? = nil
var age: Int? = nil
Unwrapping the Variable
Nil-Coalescing
// if the result is "nil", prints "Anonymous"
struct Book {
let title: String
let author: String?
}
let book = Book(title: "Beowulf", author: nil)
let author = book.author ?? "Anonymous"
print(author)sw
// print: Anonymous
// if the result is "nil", prints "0"
let input = ""
let number = Int(input) ?? 0
print(number)
// print: 0
let names1 = ["Arya", "Bran", "Robb", "Sansa"]
let names2 = [String]()
let chosen1 = names1.randomElement()?.uppercased() ?? "No one"
print("Next in line: \(chosen1)")
// print: BRAN
let chosen2 = names2.randomElement()?.uppercased() ?? "No one"
print("Next in line: \(chosen2)")
// print: No one
struct Book {
let title: String
let author: String?
}
var book: Book? = nil
let author = book?.author?.first?.uppercased() ?? "A"
print(author)
// print: A
