CODEWITHSUNDEEP
swift
Rajesh
Rajesh

Reputation: 556

Properties inside protocols in Swift

Im learning swift. I need to ask what is the real use of properties when it is declared in protocol ? 

import UIKit

protocol parentProtocol
{
    var firstName:String {get}
    func fullName() -> String
}

class childClass:parentProtocol
{
    var firstName = ""
    func fullName() -> String {
        firstName = "rajesh darak"
        return firstName
    }
}

var c = childClass()
c.fullName()

Though I'm declaring firstName as get (i.e read only), in the function itself I'm able to change the value of firstName.

Upvotes: 0

Views: 73

Answers (1)

oisdk
oisdk

Reputation: 10091

The protocol parentProtocol declares a requirement: anything that conforms to it must have a property firstName that is gettable. It's not saying that anything that inherits must be only gettable.

Why would you want this behaviour? Well, it's kind of a design choice, but here's an example of where it's useful: CollectionType. CollectionType has a property count. Now, for some of the operations you want to perform on CollectionTypes, you need to have access to count. However, there's no need to confine things that inherit from it. For instance, Array's count is read-only:

var ar = [1, 2, 3]

ar.count = 5 // What's supposed to happen here?!

But that doesn't mean that every CollectionType has to have a read-only count. Repeat, for instance has a variable count:

var re = Repeat(count: 3, repeatedValue: 0)   // [0, 0, 0]

re.count = 5                                  // [0, 0, 0, 0, 0]

And it makes total sense for you to be able to change it.

Upvotes: 1

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