Swift: Associated types. Constraints.

Now that we’ve seen how an associated type could work in a real case example it’s time to dive a bit deeper into the available possibilities.

Let’s continue with our example showed earlier for defining a Collection:

protocol Collection {
    associatedtype Item
    var count: Int { get }
    subscript(index: Int) -> Item { get }
    mutating func append(_ item: Item)
}

What if we want to compare the appending item to any of the existing items before inserting? We need to have a way to compare for equity.

We can do this by constraining the associated type to, in this case, the Equatableprotocol:

protocol Collection {
    // The associated type now needs to conform to Equatable
    associatedtype Item: Equatable

    var count: Int { get }
    subscript(index: Int) -> Item { get }
    mutating func append(_ item: Item)
}

Associated types in Swift Protocols.
Declaration
Example
Contraints
Conforming a protocol to a protocol

Contacts
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