Error protocol conformance in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean for a type to conform to the Error protocol in Swift?

Conforming to the Error protocol means the type can be used to represent errors that can be thrown and caught in Swift's error handling system.

beginner

How do you declare a custom error type in Swift?

You declare an enum or struct that conforms to the Error protocol. For example:<br>

enum MyError: Error { case badInput case networkFailure }

intermediate

Can any type conform to the Error protocol in Swift?

Yes, any type (enum, struct, or class) can conform to Error. But enums are preferred because they clearly define distinct error cases.

intermediate

Why is it useful to conform to the Error protocol instead of using strings for errors?

Conforming to Error allows Swift's error handling system to work with your errors, enabling throw, try, and catch with type safety and better code clarity.

beginner

What happens if you throw a value that does not conform to Error?

Swift will not compile the code because only types conforming to Error can be thrown. This ensures only valid error types are used.

Which Swift type is most commonly used to define custom errors conforming to Error?

A class

B enum

C tuple

D array

Enums are preferred for defining custom errors because they clearly list distinct error cases.

What keyword is used to indicate a function can throw an error in Swift?

A error

B throwable

C throws

D try

The throws keyword marks a function that can throw an error.

What protocol must a type conform to in order to be thrown as an error?

A Catchable

B Throwable

C Exception

D Error

Only types conforming to the Error protocol can be thrown.

Which of these is a valid way to define a custom error in Swift?

A enum MyError: Error { case invalidInput }

B struct MyError { case invalidInput }

C class MyError { func error() {} }

D let MyError = "error"

An enum conforming to Error with cases is the correct way.

What happens if you try to throw a String directly in Swift?

A Compilation error

B Runs without error

C Runtime error

D Warning only

Only types conforming to Error can be thrown, so throwing a String causes a compile error.

Explain how to create and use a custom error type in Swift that conforms to the Error protocol.

Think about how you list error cases and how Swift expects errors to be thrown and caught.

Why is conforming to the Error protocol important for error handling in Swift?

Consider what Swift's error system requires to work properly.