# Protocol Oriented Programming (iOS)

> Protocols, extensions, default implementations, PATs, protocol composition, type erasure

- 20 interview questions
- Mid-Level
- [Interview Questions: iOS](https://sharpskill.dev/en/technologies/ios/interview-questions.md)

## 1. What is a protocol in Swift?

**Answer**

A protocol defines a set of properties and methods that a type must implement. It acts as a contract between the protocol and conforming types. Protocols enable interface definition without imposing inheritance hierarchies, promoting composition and code reusability.

## 2. What is protocol conformance?

**Answer**

Conformance means a type (class, struct, or enum) implements all required properties and methods from a protocol. A type can conform to multiple protocols simultaneously. Conformance establishes a type relationship independent of inheritance.

## 3. What is a protocol extension?

**Answer**

A protocol extension provides default implementations for protocol methods. All conforming types receive these implementations automatically without redefining them. This promotes code reuse and significantly reduces boilerplate.

## 17 more questions available

- How to define a protocol with a required property?
- What is protocol inheritance?

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## Other iOS interview topics

- [Swift Basics](https://sharpskill.dev/en/technologies/ios/interview-questions/swift-basics.md): 25 questions, Junior
- [Swift Language Essentials](https://sharpskill.dev/en/technologies/ios/interview-questions/swift-language-essentials.md): 15 questions, Junior
- [UIKit Fundamentals](https://sharpskill.dev/en/technologies/ios/interview-questions/uikit-fundamentals.md): 18 questions, Junior
- [UIViewController Lifecycle](https://sharpskill.dev/en/technologies/ios/interview-questions/uiviewcontroller-lifecycle.md): 20 questions, Junior
- [UserDefaults & Keychain](https://sharpskill.dev/en/technologies/ios/interview-questions/userdefaults-keychain.md): 20 questions, Junior
- [Application Lifecycle](https://sharpskill.dev/en/technologies/ios/interview-questions/app-lifecycle.md): 20 questions, Junior
- [Auto Layout & Constraints](https://sharpskill.dev/en/technologies/ios/interview-questions/auto-layout-constraints.md): 24 questions, Mid-Level
- [UITableView & UICollectionView](https://sharpskill.dev/en/technologies/ios/interview-questions/uitableview-uicollectionview.md): 25 questions, Mid-Level
- [SwiftUI Basics](https://sharpskill.dev/en/technologies/ios/interview-questions/swiftui-basics.md): 18 questions, Mid-Level
- [SwiftUI State Management](https://sharpskill.dev/en/technologies/ios/interview-questions/swiftui-state-management.md): 22 questions, Mid-Level
- [SwiftUI Navigation](https://sharpskill.dev/en/technologies/ios/interview-questions/swiftui-navigation.md): 18 questions, Mid-Level
- [Networking & URLSession](https://sharpskill.dev/en/technologies/ios/interview-questions/networking-urlsession.md): 20 questions, Mid-Level
- [Codable & JSON Parsing](https://sharpskill.dev/en/technologies/ios/interview-questions/codable-json-parsing.md): 20 questions, Mid-Level
- [Core Data](https://sharpskill.dev/en/technologies/ios/interview-questions/core-data.md): 22 questions, Mid-Level
- [MVVM Architecture](https://sharpskill.dev/en/technologies/ios/interview-questions/mvvm-architecture.md): 20 questions, Mid-Level
- [Push Notifications](https://sharpskill.dev/en/technologies/ios/interview-questions/push-notifications.md): 18 questions, Mid-Level
- [Unit Testing & XCTest](https://sharpskill.dev/en/technologies/ios/interview-questions/unit-testing-xctest.md): 20 questions, Mid-Level
- [UI Testing](https://sharpskill.dev/en/technologies/ios/interview-questions/ui-testing.md): 18 questions, Mid-Level
- [Xcode & Build System](https://sharpskill.dev/en/technologies/ios/interview-questions/xcode-build-system.md): 16 questions, Mid-Level
- [Swift Package Manager](https://sharpskill.dev/en/technologies/ios/interview-questions/swift-package-manager.md): 16 questions, Mid-Level
- [Memory Management & ARC](https://sharpskill.dev/en/technologies/ios/interview-questions/memory-management-arc.md): 22 questions, Senior
- [Combine Framework](https://sharpskill.dev/en/technologies/ios/interview-questions/combine-framework.md): 24 questions, Senior
- [Concurrency & async/await](https://sharpskill.dev/en/technologies/ios/interview-questions/concurrency-async-await.md): 26 questions, Senior
- [iOS Design Patterns](https://sharpskill.dev/en/technologies/ios/interview-questions/ios-design-patterns.md): 24 questions, Senior
- [Performance Optimization](https://sharpskill.dev/en/technologies/ios/interview-questions/performance-optimization.md): 22 questions, Senior
- [Security & Encryption](https://sharpskill.dev/en/technologies/ios/interview-questions/security-encryption.md): 20 questions, Senior
- [SwiftUI Advanced](https://sharpskill.dev/en/technologies/ios/interview-questions/swiftui-advanced.md): 22 questions, Senior
- [iOS Application Architecture](https://sharpskill.dev/en/technologies/ios/interview-questions/ios-app-architecture.md): 22 questions, Senior

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