swift4: deeper dive- optionals

Currently enrolled in Udemy’s- The Complete iOS 11 & Swift Developer Course Notes from Lesson 4

What are Optionals?

• optionals are used when a value may be absent (nil)
• indicated by the ? on the type of the variable
  • e.g. var myOptional: Int?
• to access the raw value from an optional, you unwrap it by !
  • e.g. myOptional!

What’s a Great Example of Where Optionals Occur?

• a great example is using ui text fields because it is not always guaranteed that the user will enter a value. If you assume that the user will always input a value, the swift compiler will error.

• this will error out because we’re assuming that the inputNumber has a text value and then casting it to an Int

• the error you will see is: Value of optional type ‘String?’ not unwrapped; did you mean to use ‘!’ or ‘?’?

  @IBOutlet weak var myUITextField: UITextField!
  
  @IBAction func myAction(_ sender: Any) {
      if let inputNumber = Int(myUITextField.text) {
          print("sum is: \(inputNumber + 100)")
      }
  

• to fix this, use if let to check if the value exists before casting it to an Int

  @IBOutlet weak var myUITextField: UITextField!
  
  if let inputText = myUITextField.text {
    if let inputNumber = Int(inputText) {
      print("sum is: \(inputNumber + 100)")
    } else {
      print("Oops no input text to sum")
    }
  }