Why is the "let" necessary in the if-let statement? Wouldn't if just work fine without it? Why make it a constant?

Hello William,

When to use “if let”?

If let is a special structure in Swift that allows you to check if an Optional holds a value, and in case it does – do something with the unwrapped value. Let’s have a look:

if let nav = controller.navigationController {
    nav.pushViewController(myViewController, animated: true)
} else {
    //show an alert ot something else
}

The if let structure unwraps controller.navigationController (i.e. checks if there’s a value stored and takes that value) and stores its value in the nav constant. You can use nav inside the first branch of the if. Notice that inside the if you don’t need to use ? or ! anymore. It’s important to realize that nav is actually of type UINavigationController that’s not an Optional type so you can use its value directly. (If you remember in contrast the navigationController’s original type is UINavigationController?)

if let is useful also in another case. Imagine that instead of a single method call you want to do more stuff with your navigationController. If you do not use if let you code will looke like this:

controller.navigationController?.hidesBarsOnSwipe = true
controller.navigationController?.hidesBarsOnTap = true
controller.navigationController?.navigationBarHidden = false
controller.navigationController?.popToRootViewControllerAnimated(true)

This code works but you need to unwrap the property 4 times and the code gets quite repetitive. It’s much cleaner and nicer (and faster) to unwrap the value once in an if let:

if let nav = controller.navigationController {
  nav.hidesBarsOnSwipe = true
  nav.hidesBarsOnTap = true
  nav.navigationBarHidden = false
  nav.popToRootViewControllerAnimated(true)
}

Much nicer, isn’t it?

If you liked to learn more check out this post.