18.0 Protocols
A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality. The protocol can then be adopted by a class, structure, or enumeration to provide an actual implementation of those requirements. Any type that satisfies the requirements of a protocol is said to conform to that protocol.
In addition to specifying requirements that conforming types must implement, you can extend a protocol to implement some of these requirements or to implement additional functionality that conforming types can take advantage of.
Protocols are declared using the protocol keyword:
protocol SomeProtocol {
// protocol definition goes here
}A type says that it implements a protocol by placing a colon after its name. Multiple protocols can be specified, and are seperated by colons:
struct SomeStructure: FirstProtocol, AnotherProtocol {
// structure definition goes here
}If a class has a superclass, list the superclass name before any protocols it adopts:
class SomeClass: SomeSuperclass, FirstProtocol, AnotherProtocol {
// class definition goes here
}