errorfmt

README

Package errorfmt annotates Go error values.

https://kr.dev/errorfmt

Documentation

Overview

Package errorfmt provides a helper function to decorate errors with additional context.

Index

• func Handlef(format string, a ...interface{})

Examples

• Handlef

Functions

func Handlef

func Handlef(format string, a ...interface{})

Handlef decorates an error with additional context. Its behavior is almost the same as fmt.Errorf, with a few differences:

1. There must be exactly one *error argument.
2. Instead of returning a value, Handlef assigns its result via this pointer, to update the error in place.
3. The *error is dereferenced before formatting. (Therefore, verb %w also accepts *error.)
4. If it points to a nil error, Handlef does nothing.

These differences make it more convenient to use Handlef in a defer statement at the top of a block.

Example

package main

import (
	"errors"
	"fmt"

	"kr.dev/errorfmt"
)

func main() {
	err := Frob("baz")
	if err != nil {
		fmt.Println(err)
	}
}

func Frob(name string) (err error) {
	defer errorfmt.Handlef("frob widget %s: %w", name, &err)

	err = step1()
	if err != nil {
		return err
	}

	err = step2()
	if err != nil {
		return err
	}
	return nil
}

func step1() error { return nil }
func step2() error { return errors.New("step2 failed") }

Output:

frob widget baz: step2 failed