What is a nested class or nested struct?

Paul Hudson    February 12th 2018    @twostraws

Nested types – i.e. nested structs and nested classes – are a useful way of organizing your code, and perhaps even restricting what others can do with it. In essence, a nested type is just one data type defined inside another, like this:

struct Deck {
    struct Card {

    }
}

Now rather than creating a new Card struct you would instead create a new Deck.Card because one is inside the other.

This approach is useful for organizing larger applications, because you might need custom types that are applicable only in certain places – exposing them elsewhere might cause problems.

If you want to re-enforce this, Swift lets you mark the inner type (Card above) as being private, which means it can only be used inside the Deck class – code from outside Deck can’t even see it.

Available from iOS 8.0 – learn more in my book Pro Swift

Did this solution work for you? Please pass it on!

Tweet

Other people are reading…

• How to swap two items in an array using swapAt()
• What is the @objcMembers attribute?
• How to delay execution of code using the defer keyword
• How to specify your own date format with Codable and JSONEncoder
• How to constrain a protocol associated type

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.