Learning Test-Driven Development with Go/

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Error Handling

Error Handling

Learn about errors in Go.

We'll cover the following...

Errors in Go

Errors are normal values within Go. We can deal with them in the same way we deal with other types, such as int, string, bool, and so on.

How we can define an error

There are three different ways we can define an error:

  • By implementing the error interface
  • By calling the errors.New() function
  • By calling the fmt.Errorf() function

Let’s see the first two methods in action in the code snippet below:

Go (1.18.2)
package main
import (
	"errors"
	"fmt"
)
// 1. defining struct for error
type CustomErr struct {
	Code     string
	ErrorMsg string
}
// 2. implement error interface
func (c *CustomErr) Error() string {
	return fmt.Sprintf("code: %q\nmessage: %q", c.Code, c.ErrorMsg)
}
func Divide(a, b int) (int, error) {
	if b == 0 {
		// 3. return our custom error
		return 0, &CustomErr{Code: "INVALID", ErrorMsg: "cannot divide by 0"}
	}
	return a / b, nil
}
func main() {
	a, b := 3, 0
	_, err := Divide(a, b)
	if err != nil {
		// 4. run the Error() method on error returned
		fmt.Println(err.Error())
		// 5. other method to create an error
		err = errors.New("sample error")
		fmt.Println(err.Error())
		return
	}
}

In the example, the program checks for the error and eventually prints it to the console.

defer, panic, and recover

In this snippet below, we see three keywords. The ...