Error Handling in Go

Posted by yhuang

Public (Editable by Users)

In Go it’s idiomatic to communicate errors via an explicit, separate return value. This contrasts with the exceptions used in languages like Java and Ruby and the overloaded single result / error value sometimes used in C. Go’s approach makes it easy to see which functions return errors and to handle them using the same language constructs employed for any other, non-error tasks.

Language Go

Dependencies

Edit

main.go

package main

import (
    "errors"
    "fmt"
)

// By convention, errors are the last return value and have the type error, a built-in interface.
func f1(arg int) (int, error) {
    if arg == 42 {
        // errors.New constructs a basic error value with the given error message.
        return -1, errors.New("can't work with 42")
    }
    // A nil value in the error position indicates that there was no error.
    return arg + 3, nil
}

// Custom error types implement the the "Error() string" signature.
type argError struct {
    arg  int
    prob string
}

func (e *argError) Error() string {
    return fmt.Sprintf("%d - %s", e.arg, e.prob)
}

func f2(arg int) (int, error) {
    if arg == 42 {

        return -1, &argError{arg, "can't work with it"}
    }
    return arg + 3, nil
}

func main() {

    for _, i := range []int{7, 42} {
        if r, e := f1(i); e != nil {
            fmt.Println("f1 failed:", e)
        } else {
            fmt.Println("f1 worked:", r)
        }
    }
    for _, i := range []int{7, 42} {
        if r, e := f2(i); e != nil {
            fmt.Println("f2 failed:", e)
        } else {
            fmt.Println("f2 worked:", r)
        }
    }

    _, e := f2(42)
    if ae, ok := e.(*argError); ok {
        fmt.Println(ae.arg)
        fmt.Println(ae.prob)
    }
}

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