CODEWITHSUNDEEP
swiftprotocolsdefaultimplementationextends
user4956851
user4956851

Reputation:

How to instantiate default implementation of Protocol fully defined by Extensions

Would you like to explain me what's wrong in this code? I'm trying to understand the protocols' default implementation

protocol Person {
  var name: String {get}
  func printName() -> String
}

extension Person {
  var name: String {
    return "Andrea"
  }
}

extension Person {
  func printName() -> String {
      return "\(name) bye bye"
  }
}

struct person: Person {} //correct

person.name  // error

person.printName() // error

Upvotes: 0

Views: 111

Answers (3)

Sam Fischer
Sam Fischer

Reputation: 1472

Protocols are not data types. You are trying to use it as a data type in this line :

struct person: Person {}

Instead, you should use a struct/enum/class that conforms to a protocol.

In your case, the optimum solution would be to use struct :

struct PersonStruct: Person {}
let foo = PersonStruct()
print(foo.name)
foo.printName()

Upvotes: 0

BaseZen
BaseZen

Reputation: 8718

You're confusing types and values.

struct person is a new type that adopts the Person protocol.

Now you need to define an instance.

This should be clearer:

protocol PersonProtocol {
    var name: String {get}
    func printName() -> String
}

extension PersonProtocol {
    var name: String {
        return "Andrea"
    }
}

extension PersonProtocol {
    func printName() -> String {
        return "\(name) bye bye"
    }
}

struct ConcretePersonType: PersonProtocol { } // correct

var personInstance = ConcretePersonType()

print(personInstance.name)  // No more error!

personInstance.printName() // No more error!

Upvotes: 4

Yury
Yury

Reputation: 6114

You try to use static methods that not exist; make instance of struct instead:

struct Friend: Person {}

let friend = Friend()
print(friend.name)
friend.printName()

Upvotes: 2

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