errors

Documentation

Overview

Package errors provides a consistent interface for using errors. It also supports slog structured logging attributes; i.e. structured errors. It is also a drop-in replacement for the standard library errors package.

Index

• func As(err error, target any) bool
• func Cause(err error) error
• func Is(err, target error) bool
• func New(msg string, attrs ...any) error
• func NewSentinel(msg string) error
• func Unwrap(err error) error
• func Wrap(err error, msg string, attrs ...any) error

Functions

func As

func As(err error, target any) bool

As finds the first error in err's chain that matches target, and if so, sets target to that error value and returns true.

The chain consists of err itself followed by the sequence of errors obtained by repeatedly calling Unwrap.

An error matches target if the error's concrete value is assignable to the value pointed to by target, or if the error has a method As(any) bool such that As(target) returns true. In the latter case, the As method is responsible for setting target.

As will panic if target is not a non-nil pointer to either a type that implements error, or to any interface type. As returns false if err is nil.

func Cause

func Cause(err error) error

Cause calls Unwrap until it finds the root cause of the error.

func Is

func Is(err, target error) bool

Is reports whether any error in err's chain matches target.

The chain consists of err itself followed by the sequence of errors obtained by repeatedly calling Unwrap.

An error is considered to match a target if it is equal to that target or if it implements a method Is(error) bool such that Is(target) returns true.

func New

func New(msg string, attrs ...any) error

New returns an error that formats as the given text and contains the structured (slog) attributes and stack trace.

func NewSentinel

func NewSentinel(msg string) error

NewSentinel returns a new error that formats as the given text. It doesn't contain a stack trace. This can be used to support error checking with proper runtime stack traces.

// ErrNotFound is a sentinel error, it doesn't have a stack trace.
var ErrNotFound = errors.NewSentinel("not found")

// Foo returns a sentinel error with runtime stack trace of this function
// instead of the stack trace of ErrNotFound initialization.
func Foo() error {
  return errors.Wrap(ErrNotFound, "foo failed")
}

// Usage
if errors.Is(Foo(), ErrNotFound) {
  // Handle ErrNotFound or log it with proper runtime stack traces.

func Unwrap

func Unwrap(err error) error

Unwrap returns the result of calling the Unwrap method on err, if err's type contains an Unwrap method returning error. Otherwise, Unwrap returns nil.

func Wrap

func Wrap(err error, msg string, attrs ...any) error

Wrap returns a new error wrapping the provided with additional structured fields.