Is it possible to define a default implementation of a method in an interface or protocol?

In Swift, protocols can contain default method implementations through extensions. This allows setting a default behavior for protocol methods, which can be overridden in specific types.

Example:

protocol Greetable {
    func greet()
}

extension Greetable {
    func greet() {
        print("Default greeting")
    }
}

struct Person: Greetable {}

let p = Person()
p.greet() // Will output: Default greeting

Thus, the default implementation is set not in the protocol itself, but in its extension.