Can you explain the concept of a linked type in the context of typing?

Associated type — is a concept in type systems, often found in programming languages with generics, such as Swift.

It allows a protocol (interface) to declare a placeholder for a type, which will be specified by a concrete type implementing that protocol. This provides flexibility and enables the creation of more abstract and reusable constructs.

For example, in Swift:

protocol Container {
    associatedtype Item
    func append(_ item: Item)
    var count: Int { get }
    subscript(i: Int) -> Item { get }
}

Here, Item is an associated type that the specific container will define itself (for example, an array might define Item as Int or any other type).

Thus, an associated type allows protocols to be generic while still retaining information about the specific types they work with.