Protocol composition in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is protocol composition in Swift?

Protocol composition lets you combine multiple protocols into one requirement. It means a type must conform to all listed protocols.

beginner

How do you write a protocol composition type in Swift?

Use the ampersand (&) symbol between protocols, like ProtocolA & ProtocolB.

intermediate

Why use protocol composition instead of a single protocol?

It allows flexibility by combining existing protocols without creating a new one. You can require multiple behaviors at once.

beginner

Example: What does this mean?<br>func performAction(with object: ProtocolA & ProtocolB)

The function accepts an object that conforms to both ProtocolA and ProtocolB. The object must implement all requirements from both.

intermediate

Can protocol composition be used with class and protocol types?

Yes. You can combine protocols and also require a class type by adding <code>AnyObject</code> in the composition, like <code>ProtocolA & AnyObject</code>.

How do you combine two protocols, ProtocolA and ProtocolB, in Swift?

A ProtocolA & ProtocolB

B ProtocolA | ProtocolB

C ProtocolA + ProtocolB

D ProtocolA, ProtocolB

Use the ampersand (&) to combine protocols in Swift.

What does a function parameter typed as ProtocolA & ProtocolB require?

A An object conforming to ProtocolA only

B An object conforming to either ProtocolA or ProtocolB

C An object conforming to both ProtocolA and ProtocolB

D An object conforming to ProtocolB only

The object must conform to all protocols in the composition.

Can protocol composition include class type constraints?

A Yes, by including AnyObject in the composition

B No, only protocols can be composed

C Yes, by using class keyword inside composition

D No, class types are separate

Including AnyObject restricts the composition to class types.

Why might you use protocol composition instead of defining a new protocol?

A To inherit from multiple classes

B To create a new class

C To override protocol methods

D To avoid code duplication and combine existing protocols

Protocol composition combines existing protocols without creating a new one.

Which of these is NOT a valid protocol composition in Swift?

A ProtocolA & AnyObject

B ProtocolA | ProtocolB

C ProtocolA & ProtocolB

D ProtocolA & ProtocolB & AnyObject

The | symbol is not used for protocol composition in Swift.

Explain what protocol composition is and how it is used in Swift.

Think about how you can require multiple behaviors at once.

Describe a situation where protocol composition is better than creating a new protocol.

Consider when you want to require multiple capabilities without new names.