Existential types (any keyword) in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an existential type in Swift?

An existential type is a type that can hold any value conforming to a specific protocol or set of protocols. It allows you to work with values of different types through a common interface.

beginner

What does the any keyword do in Swift?

The any keyword explicitly marks a type as an existential type, meaning it can hold any value conforming to the specified protocol. It clarifies that the value is not a specific type but any type that fits the protocol.

beginner

How do you declare a variable that can hold any type conforming to a protocol Drawable using the any keyword?

You declare it like this: <br>var shape: any Drawable<br>This means shape can hold any value that conforms to the Drawable protocol.

intermediate

Why did Swift introduce the any keyword for existential types?

Swift introduced any to make it clear when a type is existential, improving code readability and safety by distinguishing between concrete types and existential types.

intermediate

Can you use existential types with multiple protocols? How?

Yes, you can combine multiple protocols using the any keyword like this: <br>var value: any ProtocolA & ProtocolB<br>This means value can hold any type conforming to both ProtocolA and ProtocolB.

What does the any keyword in Swift indicate?

A A type alias

B A concrete type is used

C A generic type parameter

D A value can be any type conforming to a protocol

The any keyword marks a type as existential, meaning it can hold any value conforming to the specified protocol.

Which of the following is a correct way to declare an existential type variable for protocol Equatable?

A var item: Equatable

B var item: <Equatable>

C var item: any Equatable

D var item: Equatable & any

Using any Equatable explicitly declares an existential type variable.

Why is using any keyword recommended over omitting it for existential types?

A It improves code clarity and safety

B It makes code run faster

C It allows inheritance

D It disables protocol conformance

The any keyword makes it clear the type is existential, improving readability and safety.

Can you assign a value of a concrete type conforming to a protocol to a variable declared as any Protocol?

A No, only existential types are allowed

B Yes, because the variable accepts any conforming type

C Only if the concrete type is a class

D Only if the concrete type is a struct

Existential types can hold any value conforming to the protocol, including concrete types.

How do you declare a variable that conforms to both Codable and Hashable using existential types?

A var data: any Codable & Hashable

B var data: Codable & Hashable

C var data: any Codable, Hashable

D var data: Codable | Hashable

You combine protocols with & and prefix with any to declare an existential type conforming to multiple protocols.

Explain what existential types are in Swift and how the any keyword is used with them.

Think about how you can hold different types that share a protocol.

Describe the benefits of using the any keyword explicitly in your Swift code.

Why does Swift want you to write <code>any</code> now?