Swift Tip: Initializing & configuring properties

This article is also published on my blog.

Sometimes, you need to do more than just assign a value to a property on initialization.

class Foo {
    let formatter = DateFormatter()
}

You might need to configure some of the properties. The first thing that comes to your mind is probably doing it in an initializer.

class Foo {
    let formatter = DateFormatter()

    init() {
        formatter.dateStyle = .short
    }
}

There are more ways how to configure your properties without putting the code in the initializer.

class Foo {
    let formatter: DateFormatter = {
        $0.dateStyle = .short
        return $0
    }(DateFormatter())
}

In the example above, you can see that the property Foo.formatter is constructed with a closure which takes the instance of DateFormatter as a parameter. You can do the same with initializing the DateFormatter directly in the closure:

class Foo {
    let formatter: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateStyle = .short
        return formatter
    }()
}

You can also use a function or a static method to construct the property.

func dateFormatter() -> DateFormatter {
    let formatter = DateFormatter()
    formatter.dateStyle = .short
    return formatter
}

class Foo {
    let formatter: DateFormatter = dateFormatter()
}

class Foo {
    let formatter: DateFormatter = Foo.dateFormatter()

    static func dateFormatter() -> DateFormatter {
        let formatter = DateFormatter()
        formatter.dateStyle = .short
        return formatter
    }
}

All these options work for local variables too.

Get in touch on Twitter @zdnkt for comments, discussion feedback or ideas!

This article is also published on my blog.