Custom error types in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom error type in Go?

A custom error type in Go is a user-defined type that implements the error interface by having an Error() string method. It allows you to create errors with additional context or behavior beyond the basic error message.

beginner

How do you define a custom error type in Go?

You define a custom error type by creating a struct or type and implementing the Error() string method on it. For example:<br>

type MyError struct { Msg string }
func (e MyError) Error() string { return e.Msg }

intermediate

Why use custom error types instead of plain errors?

Custom error types let you add extra information or methods to errors. This helps in identifying error causes, handling errors differently, or adding context like error codes or timestamps.

intermediate

How can you check for a specific custom error type in Go?

You can use a type assertion or errors.As to check if an error is a specific custom error type. For example:<br>

var myErr MyError
if errors.As(err, &myErr) { /* handle MyError */ }

beginner

Show a simple example of a custom error type with additional context.

Example:<br>

type NotFoundError struct { Resource string }
func (e NotFoundError) Error() string {
  return fmt.Sprintf("%s not found", e.Resource)
}

<br>This error tells which resource was not found.

What method must a custom error type implement in Go?

A Error() string

B String() string

C Message() string

D ToString() string

The error interface in Go requires the Error() string method.

Which Go feature helps you check if an error is a specific custom error type?

A Panic recovery

B Type assertion or errors.As

C Reflection only

D Interface embedding

Type assertion or errors.As lets you check and extract specific error types.

Why might you create a custom error type instead of using errors.New?

A To make errors print in uppercase

B To make errors faster

C To avoid using the error interface

D To add extra information or behavior to the error

Custom error types allow adding context or methods to errors.

What is the return type of the Error() method in a custom error type?

A string

B int

C bool

D error

The Error() method returns a string describing the error.

Which of these is a valid custom error type declaration in Go?

A var MyError = errors.New("error")

B func MyError() error { return "error" }

C type MyError struct { Msg string }

D type MyError int

A struct with fields is a common way to define a custom error type.

Explain how to create and use a custom error type in Go.

Think about how Go's error interface works and how you can add extra info.

Why are custom error types useful in Go programming?

Consider real-life situations where knowing more about an error helps.