Type erasure concept in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is type erasure in Swift?

Type erasure is a technique to hide specific type information behind a common interface, allowing different types to be treated uniformly without exposing their concrete types.

beginner

Why do we use type erasure in Swift?

We use type erasure to work around limitations of protocols with associated types or self requirements, enabling us to store or pass around heterogeneous types that conform to the same protocol.

intermediate

How does a AnySequence in Swift demonstrate type erasure?

AnySequence hides the concrete sequence type and exposes a uniform interface, so you can use different sequence types interchangeably without knowing their exact types.

intermediate

What is a common pattern to implement type erasure in Swift?

Create a wrapper struct or class that conforms to the protocol and holds a private instance of the concrete type. The wrapper forwards calls to the underlying instance, hiding its type.

beginner

Give a simple example of type erasure in Swift.

A wrapper like AnyHashable erases the type of any hashable value, allowing you to store different hashable types in a single collection.

What problem does type erasure solve in Swift?

A Allows hiding concrete types behind a common interface

B Improves runtime performance by avoiding type checks

C Automatically converts types to strings

D Prevents memory leaks in closures

Type erasure hides concrete types so different types can be used uniformly through a common interface.

Which Swift feature often requires type erasure to be used?

A Protocols with associated types

B Classes with inheritance

C Global functions

D Stored properties

Protocols with associated types cannot be used as types directly, so type erasure helps to work around this.

What does AnySequence do in Swift?

A Sorts sequences alphabetically

B Creates a new sequence type

C Erases the type of any sequence

D Converts sequences to arrays

AnySequence erases the concrete sequence type, allowing different sequences to be used interchangeably.

How is type erasure typically implemented?

A By subclassing all types

B Using a wrapper that forwards calls to the underlying type

C By using global variables

D By converting types to strings

A wrapper struct or class forwards protocol calls to the hidden concrete type, implementing type erasure.

Which of these is an example of a type-erased wrapper in Swift?

A Int

B Array

C String

D AnyHashable

AnyHashable erases the type of any hashable value, allowing heterogeneous collections.

Explain type erasure in Swift and why it is useful.

Think about protocols with associated types and how you can use different types together.

Describe how you would implement a type-erased wrapper for a protocol with an associated type.

Focus on forwarding calls and hiding the underlying type.