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errors: add example showing a custom error with Unwrap
Change-Id: I2bddee9b460d3875911859b49528a00d318f37fc Reviewed-on: https://go-review.googlesource.com/c/go/+/184237 Reviewed-by: Russ Cox <rsc@golang.org> Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
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src/errors/example_unwrap_test.go
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56
src/errors/example_unwrap_test.go
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// Copyright 2019 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package errors_test
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import (
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"errors"
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"fmt"
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"os"
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"time"
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)
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// MyError2 is an error implementation that includes a time, a message, and an
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// underlying error.
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type MyError2 struct {
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When time.Time
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What string
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err error
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}
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func (e MyError2) Error() string {
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return fmt.Sprintf("%v at %v: %v", e.What, e.When, e.err)
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}
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// Unwrap returns e's underlying error, or nil if there is none.
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func (e MyError2) Unwrap() error {
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return e.err
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}
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func readConfig() error {
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if _, err := os.Open("non-existing"); err != nil {
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return MyError2{
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time.Date(1989, 3, 15, 22, 30, 0, 0, time.UTC),
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"reading config file",
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err,
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}
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}
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return nil
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}
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func Example_unwrap() {
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if err := readConfig(); err != nil {
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// Display the error.
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fmt.Println(err)
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// If we can retrieve the path, try to recover
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// by taking another action.
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var pe *os.PathError
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if errors.As(err, &pe) {
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restoreFile(pe.Path)
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}
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}
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// Output: reading config file at 1989-03-15 22:30:00 +0000 UTC: open non-existing: no such file or directory
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}
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func restoreFile(path string) {}
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