error.go

     1  // Copyright 2011 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  // This file contains the code snippets included in "Error Handling and Go."
     6  
     7  package main
     8  
     9  import (
    10  	"encoding/json"
    11  	"errors"
    12  	"fmt"
    13  	"log"
    14  	"net"
    15  	"os"
    16  	"time"
    17  )
    18  
    19  type File struct{}
    20  
    21  func Open(name string) (file *File, err error) {
    22  	// OMIT
    23  	panic(1)
    24  	// STOP OMIT
    25  }
    26  
    27  func openFile() { // OMIT
    28  	f, err := os.Open("filename.ext")
    29  	if err != nil {
    30  		log.Fatal(err)
    31  	}
    32  	// do something with the open *File f
    33  	// STOP OMIT
    34  	_ = f
    35  }
    36  
    37  // errorString is a trivial implementation of error.
    38  type errorString struct {
    39  	s string
    40  }
    41  
    42  func (e *errorString) Error() string {
    43  	return e.s
    44  }
    45  
    46  // STOP OMIT
    47  
    48  // New returns an error that formats as the given text.
    49  func New(text string) error {
    50  	return &errorString{text}
    51  }
    52  
    53  // STOP OMIT
    54  
    55  func Sqrt(f float64) (float64, error) {
    56  	if f < 0 {
    57  		return 0, errors.New("math: square root of negative number")
    58  	}
    59  	// implementation
    60  	return 0, nil // OMIT
    61  }
    62  
    63  // STOP OMIT
    64  
    65  func printErr() (int, error) { // OMIT
    66  	f, err := Sqrt(-1)
    67  	if err != nil {
    68  		fmt.Println(err)
    69  	}
    70  	// STOP OMIT
    71  	// fmtError OMIT
    72  	if f < 0 {
    73  		return 0, fmt.Errorf("math: square root of negative number %g", f)
    74  	}
    75  	// STOP OMIT
    76  	return 0, nil
    77  }
    78  
    79  type NegativeSqrtError float64
    80  
    81  func (f NegativeSqrtError) Error() string {
    82  	return fmt.Sprintf("math: square root of negative number %g", float64(f))
    83  }
    84  
    85  // STOP OMIT
    86  
    87  type SyntaxError struct {
    88  	msg    string // description of error
    89  	Offset int64  // error occurred after reading Offset bytes
    90  }
    91  
    92  func (e *SyntaxError) Error() string { return e.msg }
    93  
    94  // STOP OMIT
    95  
    96  func decodeError(dec *json.Decoder, val struct{}) error { // OMIT
    97  	var f os.FileInfo // OMIT
    98  	if err := dec.Decode(&val); err != nil {
    99  		if serr, ok := err.(*json.SyntaxError); ok {
   100  			line, col := findLine(f, serr.Offset)
   101  			return fmt.Errorf("%s:%d:%d: %v", f.Name(), line, col, err)
   102  		}
   103  		return err
   104  	}
   105  	// STOP OMIT
   106  	return nil
   107  }
   108  
   109  func findLine(os.FileInfo, int64) (int, int) {
   110  	// place holder; no need to run
   111  	return 0, 0
   112  }
   113  
   114  func netError(err error) { // OMIT
   115  	for { // OMIT
   116  		if nerr, ok := err.(net.Error); ok && nerr.Temporary() {
   117  			time.Sleep(1e9)
   118  			continue
   119  		}
   120  		if err != nil {
   121  			log.Fatal(err)
   122  		}
   123  		// STOP OMIT
   124  	}
   125  }
   126  
   127  func main() {}
   128
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