Type Casting in swift

Question

I am bit confused with typecasting in Swift.

Have a small doubt. What is the difference between as?,as! and only as. And can we say "as" is similar to is.

Thanks in advance.

Answer 1

The 'as' keyword is used for casting.

'as' example:

let calcVC = destinationViewController as CalculatorViewController

This line casts the destinationViewController to a CalculatorViewController. However, this would crash if destinationViewController was not a CalculatorViewController or a subclass thereof.

To protect against a crash, you can use 'if let' with 'as?'...

'as?' example:

if let calcVC = destinationViewController as? CalculatorViewController {
   // ... write code to execute if destinationViewController is in fact a CalculatorViewController
}

You can even check before you even try to do 'as' with the 'is' keyword...

'is' example:

if destinationViewController is CalculatorViewController {
   //...
}