Errors

import "errors"

Package errors implements functions to manipulate errors…

Package Index

There is only one function so far…

func New

func New(text string) error

New returns an error that formats as the given text.

Example Usage and Notes

• Return as error

Just call *New* with a short description of the error

f, err := os.Open(path)
if err != nil {
   return nil, errors.New("open failed")
} 
defer f.Close()

• Save as variable and reuse

Save the result struct in a variable and reuse it when needed

var OpenFailed = errors.New("open failed")
func ReadFile(path string) ([]byte, error) {
    f, err := os.Open(path)
    if err != nil {
       return nil, OpenFailed
    }
    defer f.Close()
    ...
}

• A note about error strings from Go Code Review Guide

Error strings should not be capitalized (unless beginning with proper nouns or acronyms) or end with punctuation, since they are usually printed following other context.

That is, use fmt.Errorf("something bad") not fmt.Errorf("Something bad"), so that log.Printf("Reading %s: %v", filename, err) formats without a spurious capital letter mid-message.

This does not apply to logging, which is implicitly line-oriented and not combined inside other messages.

• Different allocations should not be equal

…as they create 2 different error objects

errors.New("open failed") != errors.New("open failed")

Complete example

Internally New assigns the string to a struct that implements the Error() interface.

Questions

• Why Error strings Should Not be capitalised in Go?

  Answer: Because they are usually printed following other context.

• Are 2 errors with the same message string the same?

  Answer: No, because they have different allocations.

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