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.

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This article is also published on my blog.