Swift Access Levels

private vs filePrivate vs internal vs public vs open

Assigning the appropriate access level to variables, structs, and classes in Swift is crucial for maintaining a secure and well-structured codebase. Proper access control helps ensure that internal implementation details, such as properties or methods, aren't unintentionally exposed or modified from outside their intended scope. This not only protects your code from misuse but also enhances performance and maintainability.

By restricting access to only what's necessary, you can prevent classes from being instantiated or modified in contexts where they shouldn't be used. This level of encapsulation is key to building secure, efficient, and scalable Swift applications.

Here’s a quick breakdown of different Swift access levels and their usage.

The Private Access Level.

The most restrictive access level. Accessible only within the block of code in which it was declared. I.e., within the scope of { }

private var privateVar: String?

The Fileprivate Access Level.

As the name suggests, it is private to the file. Accessible only within the .swift file in which it was declared. i.e. ViewController.swift

fileprivate var filePrivateVar: String?

The Internal Access Level.

This is the default access level given when it's not specified. Accessible anywhere inside the current app module.

var internalVar: String?  // implicitly internal

The Public Access Level.

Access is granted to any source file from its defining module, and also any source file from another module that imports the defining module.

public class SomePublicClass {}
public var somePublicVariable = 0

The Open Access Level.

Open access is the highest (least restrictive) access level. Everything in public + allows vars/classes to be subclassed and overridden outside their defining module.

Usually useful when working on frameworks and SDKs.

open class SomeOpenClass {}
open var someOpenVariable = 0

Conclusion: For standard app development, it’s generally a good practice to start with the most restrictive access level , typically private. This helps ensure that properties and functions can't be accidentally accessed or modified from outside their defining scope. In Swift, access levels should be increased only when necessary to expose functionality across different files or modules. This principle of least privilege helps keep code safer, easier to maintain, and more modular.