LESSON 635 OF 678 · OBJECT-ORIENTED PROGRAMMING

Access Modifiers in Swift

Lesson

TL ; DR:

An access modifier controls who can see a member of a class. The two you'll use most are public (anyone) and private (only this class).

Make data private so callers can't break invariants. Expose what they need through public methods (often called getters and setters):

class Dog {
    private var name: String

    init(_ name: String) {
        self.name = name
    }

    func getName() -> String {
        return name
    }
}

Outside the class, rex.name is a compile error. Use rex.getName() instead.

Full lesson:

So far every field we wrote was visible to all the code in your module (Swift's default level, internal). That's convenient, but leaks internals. If you later decide to validate or compute the value differently, every caller in the codebase breaks.

Encapsulation

Encapsulation is the idea that an object's data should be hidden behind methods. The class controls how it's read and written; outside code only sees the API.

class Account {
    private var balance: Double = 0

    func deposit(_ amount: Double) {
        if amount < 0 { fatalError("Invalid amount") }
        balance += amount
    }
}

The Swift access levels

`open` / `public`	Visible everywhere, including other modules (`open` also allows subclassing and overriding there).
`internal`	The default: visible anywhere inside the same module.
`fileprivate`	Visible only inside the same source file.
`private`	Visible only inside the enclosing declaration (and its extensions in the same file).

For now, focus on public and private.

Your task

The Dog class's name field is now private. Add a func getName() -> String method that returns it.

Dog's name: Rex

STEP 1 OF 2

Guided

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