Go has a builtin type for errors. In Go, an error is the last return value (They have type error).

The line errors.New creates a new error with a message. If there is no error, you can return the nil value.

Example

Errors

The function do() is called, which returns an error. To use Go errors, you must include the package errors: import "errors".

package main

import "errors"
import "fmt"

func do() (int, error) {
    return -1, errors.New("Something wrong")
}

func main() {
    fmt.Println( do() )
}
    
1
2
$ go run example.go
-1 Something wrong

You can combine both the return values:

r, e := do()
if r == -1 {
    fmt.Println(e)
} else {
    fmt.Print("Everything went fine\n")
}