How can you set restrictions for a communication protocol?

In iOS, the mechanism used to set communication protocol restrictions is protocols with constraints on associated types or inheritance from other protocols.

For example, you can define a protocol with type constraints to ensure that the implementing class or structure meets certain requirements:

protocol Communicable {
    associatedtype MessageType
    func send(message: MessageType)
    func receive() -> MessageType
}

// Constraint that MessageType must be String
protocol StringCommunicable: Communicable where MessageType == String {}

You can also use inheritance in protocols to restrict the set of methods or properties that must be implemented.

Thus, constraints are set through associated types with where-clauses or through protocol inheritance.