Lazy Properties in Swift

Continuing to use my blog as a reference for myself and a summary of stuff I’ve learned about here’s a post about Swift!

I’ve spent some time now trying to write a little app, and I recently wanted to set a custom dataSource on one of my tableviews. The problem was that I wanted to keep a reference to this dataSource in my table view controller (which I might actually not need since it’s always there via the tableView property). But, in Swift you need to initialize all properties in your init() which I couldn’t use since I’m relying on storyboards, so awakeFromNib() is the correct place to set such stuff up.

I first tried using optionals, ie:

class MyTableView: UITableViewController {
  let dataSource: CustomDataSource?
  
  override func awakeFromNib() {
    dataSource = CustomDataSource()
    tableView.dataSource = dataSource!
  }
}

The problem with this approach is that anytime I want to reference my dataSource I have to unwrap it using !. Which feels stupid and clumsy.

Spewing out some frustration on Twitter gave me a hint on how to properly solve this.

So after reading up on lazy my tableview controller now looks like this:

class MyTableView: UITableViewController {
  lazy var dataSource: FormalTableViewDataSource = {
    return CustomDataSource()
  }()
  
  override func awakeFromNib() {
    tableView.dataSource = dataSource
  }
}

This also works when you have a property that’s an object who’s constructor needs an object that you create after init() for example.

I’ll be super grateful if anyone tells me I’m doing it wrong :)