Model your program
Swift Protocols
Learn how protocols work in Swift to give different types a shared set of properties and methods, and how a struct or class adopts and conforms to them.
8 minute lesson
This tutorial belongs to the Swift series
A protocol is a way to have different objects, of different types, have a common set of functionality.
A protocol is defined in this way:
protocol Mammal {
}Structs and classes can adopt a protocol in this way:
struct Dog: Mammal {
}
class Cat: Mammal {
}A protocol can define properties and methods, without providing values and implementations, and a struct/class must implement them:
protocol Mammal {
var age: Int { get set }
func walk()
}The property can be defined as get or get set. If it’s get, the property must be implemented as read only, with a getter.
Any type that adopts the protocol must conform to the protocol by implementing those methods or providing those properties:
struct Dog: Mammal {
var age: Int = 0
func walk() {
print("The dog is walking")
}
}
class Cat: Mammal {
var age: Int = 0
func walk() {
print("The cat is walking")
}
}Structs and classes can adopt multiple protocols:
struct Dog: Mammal, Animal {
}
class Cat: Mammal, Animal {
}Notice that for classes, this is the same syntax used to define a superclass. If there is a superclass, list it as the first item in the list, after the colon.
Lesson completed