Protocol extensions with default implementations in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a protocol extension in Swift?

A protocol extension in Swift allows you to add methods, properties, and default implementations to a protocol. This means any type that adopts the protocol can use these default behaviors without having to implement them explicitly.

beginner

How do default implementations in protocol extensions help reduce code duplication?

Default implementations provide a shared behavior for all types conforming to the protocol. Instead of writing the same method in every conforming type, you write it once in the protocol extension, and all conforming types get it automatically.

intermediate

Can a conforming type override a default implementation provided by a protocol extension?

Yes, a conforming type can provide its own implementation of a method or property, which will override the default implementation from the protocol extension.

intermediate

What happens if a method is declared in a protocol and also implemented in its extension, but a conforming type provides its own implementation?

The conforming type's implementation is used instead of the default one from the protocol extension. This allows customization while still benefiting from default behavior when no custom implementation is provided.

intermediate

Why can't protocol extensions add stored properties?

Protocol extensions can only add computed properties or methods because protocols don't have storage. Stored properties require memory allocation, which is only possible in concrete types, not protocols.

What is the main benefit of using default implementations in protocol extensions?

A To prevent conforming types from overriding methods

B To force all conforming types to implement the method

C To add stored properties to protocols

D To provide shared behavior to all conforming types without rewriting code

Default implementations allow shared behavior so conforming types don't have to write the same code repeatedly.

Can a conforming type override a method provided by a protocol extension?

A Yes, it can provide its own implementation

B Only if the method is marked as override

C No, the default implementation is final

D Only if the protocol is a class protocol

Conforming types can always override default implementations with their own versions.

Which of the following can NOT be added in a protocol extension?

A Methods

B Computed properties

C Stored properties

D Default implementations

Protocol extensions cannot add stored properties because protocols don't have storage.

If a protocol declares a method and its extension provides a default implementation, what happens if a conforming type does NOT implement that method?

A Compilation error

B The default implementation is used

C The method is ignored

D The program crashes at runtime

The conforming type uses the default implementation from the protocol extension.

Why are protocol extensions useful in Swift?

A They provide default behavior and reduce code duplication

B They allow adding stored properties to protocols

C They enable multiple inheritance

D They replace classes

Protocol extensions provide default behavior and help avoid repeating code in multiple types.

Explain how protocol extensions with default implementations work in Swift and why they are useful.

Think about how you can write one method once and use it in many types.

Describe the limitations of protocol extensions regarding stored properties and how you can work around them.

Remember protocols don't have memory to store data.