What is behavior of private access control for swift class?

Question

I tried this with storyboard with Xcode 7 GM Seed:

import UIKit

public class C {
    let _secret = arc4random_uniform(1000)

    private func secret() -> String {
        return "\(_secret) is a secret"
    }

}
let c1 = C()
c1.secret()

This compiled and gave me the "secret". So this upsets my understanding of access control for Swift class and object. Why is this happening?

Private access restricts the use of an entity to its own defining source file. It is all documented in the Swift book, in the "Access Control" chapter. — Martin R, Sep 13 '15 at 17:43

score 3 · Accepted Answer · answered Sep 13 '15 at 17:43

In Swift private means accessible only within the same source file which is what you're doing. If the code in your question was contained in a file C.swift and you would try to access the secret method from another Swift file you would get a compile-time error.

You can read more about the different access modifiers in the official documentation.

Ahmad F · Answer 2 · 2017-10-14T16:31:44.880

Swift 4 Updated answer:

There are two different access controls: fileprivate and private.

fileprivate can be accessed from their entire files.

private can only be accessed from their single declaration and extensions.

For example:

// Declaring "A" class that has the two types of "private" and "fileprivate":
class A {
    private var aPrivate: String?
    fileprivate var aFileprivate: String?

    func accessMySelf() {
        // this works fine
        self.aPrivate = ""
        self.aFileprivate = ""
    }
}

// Declaring "B" for checking the abiltiy of accessing "A" class:
class B {
    func accessA() {
        // create an instance of "A" class
        let aObject = A()

        // Error! this is NOT accessable...
        aObject.aPrivate = "I CANNOT set a value for it!"

        // this works fine
        aObject.aFileprivate = "I CAN set a value for it!"
    }
}

For more information, check Access Control Apple's documentation, Also you could check this answer.

What is behavior of private access control for swift class?

2 Answers2