Go Error Handling Creating a custom error type
Example
In Go, an error is represented by any value that can describe itself as string. Any type that implement the built-in error interface is an error.
// The error interface is represented by a single
// Error() method, that returns a string representation of the error
type error interface {
Error() string
}
The following example shows how to define a new error type using a string composite literal.
// Define AuthorizationError as composite literal
type AuthorizationError string
// Implement the error interface
// In this case, I simply return the underlying string
func (e AuthorizationError) Error() string {
return string(e)
}
I can now use my custom error type as error:
package main
import (
"fmt"
)
// Define AuthorizationError as composite literal
type AuthorizationError string
// Implement the error interface
// In this case, I simply return the underlying string
func (e AuthorizationError) Error() string {
return string(e)
}
func main() {
fmt.Println(DoSomething(1)) // succeeds! returns nil
fmt.Println(DoSomething(2)) // returns an error message
}
func DoSomething(someID int) error {
if someID != 1 {
return AuthorizationError("Action not allowed!")
}
// do something here
// return a nil error if the execution succeeded
return nil
}
