codekingpro/portable-devtools

1// Copyright 2012 The Go Authors. All rights reserved.2// Use of this source code is governed by a BSD-style3// license that can be found in the LICENSE file.4 5package errors_test6 7import (8	"errors"9	"fmt"10	"io/fs"11	"os"12	"time"13)14 15// MyError is an error implementation that includes a time and message.16type MyError struct {17	When time.Time18	What string19}20 21func (e MyError) Error() string {22	return fmt.Sprintf("%v: %v", e.When, e.What)23}24 25func oops() error {26	return MyError{27		time.Date(1989, 3, 15, 22, 30, 0, 0, time.UTC),28		"the file system has gone away",29	}30}31 32func Example() {33	if err := oops(); err != nil {34		fmt.Println(err)35	}36	// Output: 1989-03-15 22:30:00 +0000 UTC: the file system has gone away37}38 39func ExampleNew() {40	err := errors.New("emit macho dwarf: elf header corrupted")41	if err != nil {42		fmt.Print(err)43	}44	// Output: emit macho dwarf: elf header corrupted45}46 47func OopsNew() error {48	return errors.New("an error")49}50 51var ErrSentinel = errors.New("an error")52 53func OopsSentinel() error {54	return ErrSentinel55}56 57// Each call to [errors.New] returns an unique instance of the error,58// even if the arguments are the same. To match against errors59// created by [errors.New], declare a sentinel error and reuse it.60func ExampleNew_unique() {61	err1 := OopsNew()62	err2 := OopsNew()63	fmt.Println("Errors using distinct errors.New calls:")64	fmt.Printf("Is(%q, %q) = %v\n", err1, err2, errors.Is(err1, err2))65 66	err3 := OopsSentinel()67	err4 := OopsSentinel()68	fmt.Println()69	fmt.Println("Errors using a sentinel error:")70	fmt.Printf("Is(%q, %q) = %v\n", err3, err4, errors.Is(err3, err4))71 72	// Output:73	// Errors using distinct errors.New calls:74	// Is("an error", "an error") = false75	//76	// Errors using a sentinel error:77	// Is("an error", "an error") = true78}79 80// The fmt package's Errorf function lets us use the package's formatting81// features to create descriptive error messages.82func ExampleNew_errorf() {83	const name, id = "bimmler", 1784	err := fmt.Errorf("user %q (id %d) not found", name, id)85	if err != nil {86		fmt.Print(err)87	}88	// Output: user "bimmler" (id 17) not found89}90 91func ExampleJoin() {92	err1 := errors.New("err1")93	err2 := errors.New("err2")94	err := errors.Join(err1, err2)95	fmt.Println(err)96	if errors.Is(err, err1) {97		fmt.Println("err is err1")98	}99	if errors.Is(err, err2) {100		fmt.Println("err is err2")101	}102	fmt.Println(err.(interface{ Unwrap() []error }).Unwrap())103	// Output:104	// err1105	// err2106	// err is err1107	// err is err2108	// [err1 err2]109}110 111func ExampleIs() {112	if _, err := os.Open("non-existing"); err != nil {113		if errors.Is(err, fs.ErrNotExist) {114			fmt.Println("file does not exist")115		} else {116			fmt.Println(err)117		}118	}119 120	// Output:121	// file does not exist122}123 124type MyIsError struct {125	err string126}127 128func (e MyIsError) Error() string {129	return e.err130}131func (e MyIsError) Is(err error) bool {132	return err == fs.ErrPermission133}134 135// Custom errors can implement a method "Is(error) bool" to match other error values,136// overriding the default matching of [errors.Is].137func ExampleIs_custom_match() {138	var err error = MyIsError{"an error"}139	fmt.Println("Error equals fs.ErrPermission:", err == fs.ErrPermission)140	fmt.Println("Error is fs.ErrPermission:", errors.Is(err, fs.ErrPermission))141 142	// Output:143	// Error equals fs.ErrPermission: false144	// Error is fs.ErrPermission: true145}146 147func ExampleAs() {148	if _, err := os.Open("non-existing"); err != nil {149		var pathError *fs.PathError150		if errors.As(err, &pathError) {151			fmt.Println("Failed at path:", pathError.Path)152		} else {153			fmt.Println(err)154		}155	}156 157	// Output:158	// Failed at path: non-existing159}160 161func ExampleAsType() {162	if _, err := os.Open("non-existing"); err != nil {163		if pathError, ok := errors.AsType[*fs.PathError](err); ok {164			fmt.Println("Failed at path:", pathError.Path)165		} else {166			fmt.Println(err)167		}168	}169	// Output:170	// Failed at path: non-existing171}172 173type MyAsError struct {174	err string175}176 177func (e MyAsError) Error() string {178	return e.err179}180func (e MyAsError) As(target any) bool {181	pe, ok := target.(**fs.PathError)182	if !ok {183		return false184	}185	*pe = &fs.PathError{186		Op:   "custom",187		Path: "/",188		Err:  errors.New(e.err),189	}190	return true191}192 193// Custom errors can implement a method "As(any) bool" to match against other error types,194// overriding the default matching of [errors.As].195func ExampleAs_custom_match() {196	var err error = MyAsError{"an error"}197	fmt.Println("Error:", err)198	fmt.Printf("TypeOf err: %T\n", err)199 200	var pathError *fs.PathError201	ok := errors.As(err, &pathError)202	fmt.Println("Error as fs.PathError:", ok)203	fmt.Println("fs.PathError:", pathError)204 205	// Output:206	// Error: an error207	// TypeOf err: errors_test.MyAsError208	// Error as fs.PathError: true209	// fs.PathError: custom /: an error210}211 212// Custom errors can implement a method "As(any) bool" to match against other error types,213// overriding the default matching of [errors.AsType].214func ExampleAsType_custom_match() {215	var err error = MyAsError{"an error"}216	fmt.Println("Error:", err)217	fmt.Printf("TypeOf err: %T\n", err)218 219	pathError, ok := errors.AsType[*fs.PathError](err)220	fmt.Println("Error as fs.PathError:", ok)221	fmt.Println("fs.PathError:", pathError)222 223	// Output:224	// Error: an error225	// TypeOf err: errors_test.MyAsError226	// Error as fs.PathError: true227	// fs.PathError: custom /: an error228}229 230func ExampleUnwrap() {231	err1 := errors.New("error1")232	err2 := fmt.Errorf("error2: [%w]", err1)233	fmt.Println(err2)234	fmt.Println(errors.Unwrap(err2))235	// Output:236	// error2: [error1]237	// error1238}239