Type casting in Swift Language

Type Casting

Type casting is a way to check the type of an instance, or to treat that instance as a different superclass or subclass from somewhere else in its own class hierarchy.

Type casting in Swift is implemented with the is and as operators. These two operators provide a simple and expressive way to check the type of a value or cast a value to a different type.

Downcasting

A constant or variable of a certain class type may actually refer to an instance of a subclass behind the scenes. Where you believe this is the case, you can try to downcast to the subclass type with a type cast operator (as? or as!).

Because downcasting can fail, the type cast operator comes in two different forms. The conditional form, as?, returns an optional value of the type you are trying to downcast to. The forced form, as!, attempts the downcast and force-unwraps the result as a single compound action.

Use the conditional form of the type cast operator (as?) when you are not sure if the downcast will succeed. This form of the operator will always return an optional value, and the value will be nil if the downcast was not possible. This enables you to check for a successful downcast.

Use the forced form of the type cast operator (as!) only when you are sure that the downcast will always succeed. This form of the operator will trigger a runtime error if you try to downcast to an incorrect class type. Know more.

String to Int & Float conversion : -

let numbers = "888.00"
let intValue = NSString(string: numbers).integerValue
print(intValue) // Output - 888

let numbers = "888.00"
let floatValue = NSString(string: numbers).floatValue
print(floatValue) // Output : 888.0

Float to String Conversion

let numbers = 888.00
let floatValue = String(numbers) 
print(floatValue) // Output : 888.0

// Get Float value at particular decimal point 
let numbers = 888.00
let floatValue = String(format: "%.2f", numbers) // Here %.2f will give 2 numbers after decimal points we can use as per our need
print(floatValue) // Output : "888.00"

Integer to String value

let numbers = 888
let intValue = String(numbers)
print(intValue) // Output : "888"

Float to String value

let numbers = 888.00
let floatValue = String(numbers)
print(floatValue)

Optional Float value to String

let numbers: Any = 888.00
  let floatValue = String(describing: numbers)
  print(floatValue) // Output : 888.0

Optional String to Int value

let hitCount = "100"
let data :AnyObject = hitCount
let score = Int(data as? String ?? "") ?? 0
print(score)

Downcasting values from JSON

let json = ["name" : "john", "subjects": ["Maths", "Science", "English", "C Language"]] as [String : Any]
let name = json["name"] as? String ?? ""
print(name) // Output : john
let subjects = json["subjects"] as? [String] ?? []
print(subjects) // Output : ["Maths", "Science", "English", "C Language"]

Downcasting values from Optional JSON

let response: Any = ["name" : "john", "subjects": ["Maths", "Science", "English", "C Language"]]
let json = response as? [String: Any] ?? [:]
let name = json["name"] as? String ?? ""
print(name) // Output : john
let subjects = json["subjects"] as? [String] ?? []
print(subjects) // Output : ["Maths", "Science", "English", "C Language"]

Manage JSON Response with conditions

let response: Any = ["name" : "john", "subjects": ["Maths", "Science", "English", "C Language"]] //Optional Response 

guard let json = response as? [String: Any] else {
    // Handle here nil value
    print("Empty Dictionary")
    // Do something here
    return
}
let name = json["name"] as? String ?? ""
print(name) // Output : john
let subjects = json["subjects"] as? [String] ?? []
print(subjects) // Output : ["Maths", "Science", "English", "C Language"]

Manage Nil Response with condition

let response: Any? = nil
guard let json = response as? [String: Any] else {
    // Handle here nil value
    print("Empty Dictionary")
    // Do something here
    return
}
let name = json["name"] as? String ?? ""
print(name) 
let subjects = json["subjects"] as? [String] ?? []
print(subjects)

Output : `Empty Dictionary`

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