example_test.go

Documentation: errors

     1  // Copyright 2012 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package errors_test
     6  
     7  import (
     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.
    16  type MyError struct {
    17  	When time.Time
    18  	What string
    19  }
    20  
    21  func (e MyError) Error() string {
    22  	return fmt.Sprintf("%v: %v", e.When, e.What)
    23  }
    24  
    25  func 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  
    32  func 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 away
    37  }
    38  
    39  func 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 corrupted
    45  }
    46  
    47  // The fmt package's Errorf function lets us use the package's formatting
    48  // features to create descriptive error messages.
    49  func ExampleNew_errorf() {
    50  	const name, id = "bimmler", 17
    51  	err := fmt.Errorf("user %q (id %d) not found", name, id)
    52  	if err != nil {
    53  		fmt.Print(err)
    54  	}
    55  	// Output: user "bimmler" (id 17) not found
    56  }
    57  
    58  func ExampleJoin() {
    59  	err1 := errors.New("err1")
    60  	err2 := errors.New("err2")
    61  	err := errors.Join(err1, err2)
    62  	fmt.Println(err)
    63  	if errors.Is(err, err1) {
    64  		fmt.Println("err is err1")
    65  	}
    66  	if errors.Is(err, err2) {
    67  		fmt.Println("err is err2")
    68  	}
    69  	// Output:
    70  	// err1
    71  	// err2
    72  	// err is err1
    73  	// err is err2
    74  }
    75  
    76  func ExampleIs() {
    77  	if _, err := os.Open("non-existing"); err != nil {
    78  		if errors.Is(err, fs.ErrNotExist) {
    79  			fmt.Println("file does not exist")
    80  		} else {
    81  			fmt.Println(err)
    82  		}
    83  	}
    84  
    85  	// Output:
    86  	// file does not exist
    87  }
    88  
    89  func ExampleAs() {
    90  	if _, err := os.Open("non-existing"); err != nil {
    91  		var pathError *fs.PathError
    92  		if errors.As(err, &pathError) {
    93  			fmt.Println("Failed at path:", pathError.Path)
    94  		} else {
    95  			fmt.Println(err)
    96  		}
    97  	}
    98  
    99  	// Output:
   100  	// Failed at path: non-existing
   101  }
   102  
   103  func ExampleUnwrap() {
   104  	err1 := errors.New("error1")
   105  	err2 := fmt.Errorf("error2: [%w]", err1)
   106  	fmt.Println(err2)
   107  	fmt.Println(errors.Unwrap(err2))
   108  	// Output:
   109  	// error2: [error1]
   110  	// error1
   111  }
   112
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