Series 6— Custom operators combined with localization

In this episode we are gonna use custom operator for setting localizable strings on UI components.

Note: This is just a simple example, not a real world solution.

This episode’s goal:

let label = UILabel() <- Localization.welcomeMessage
print(label.text?) // prints "Gimme some sugar."

Let’s declare Localizable protocol responsible for providing localized string:

protocol Localizable {
    var localizedString: String? { get }
}

Our localization is enumtype. Each of its case represents a key which will be used in NSLocalizedString macro.

enum Localization: String, Localizable {
    case welcomeMessage = "Gimme some sugar."
    case warningMessage = "Too much sugar!"
}

Localization enum is RawRepresentable with String as its associated type so this knowledge can be used in our default implementation of Localizable protocol.

extension Localizable
    where Self: RawRepresentable, Self.RawValue == String
{
    var localizedString: String? {
        return NSLocalizedString(rawValue, comment: "")
    }
}

Custom operator

We’re gonna use infix operator. Custom operators are not covered in this post. Read more about custom operators.

infix operator <-: AdditionPrecedence

Protocol which will provide abstraction for any object which has text: String? property. We’ll call it TextAware:

protocol TextAware: class {
    var text: String? { get set }
}

Apply <- operator to TextAware protocol:

extension TextAware {
    static func <-(left: Self, right: Localization) -> Self {
        left.text = right.localizedString
 
        return left
    }
}

Now we can extend UI components with TextAware:

extension UILabel: TextAware {}
extension UITextField: TextAware {}

And finally we can use:

let label = UILabel() <- Localization.welcomeMessage
print(label.text?) // prints "Gimme some sugar."
let textField = UITextField() <- Localization.warningMessage
print(textField.text?) // prints "Too much sugar!"

Pretty easy, isn’t it?