mirror of https://go.googlesource.com/go
88 lines
2.9 KiB
Go
88 lines
2.9 KiB
Go
// Copyright 2011 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 implements functions to manipulate errors.
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//
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// The [New] function creates errors whose only content is a text message.
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//
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// An error e wraps another error if e's type has one of the methods
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//
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// Unwrap() error
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// Unwrap() []error
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//
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// If e.Unwrap() returns a non-nil error w or a slice containing w,
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// then we say that e wraps w. A nil error returned from e.Unwrap()
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// indicates that e does not wrap any error. It is invalid for an
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// Unwrap method to return an []error containing a nil error value.
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//
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// An easy way to create wrapped errors is to call [fmt.Errorf] and apply
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// the %w verb to the error argument:
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//
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// wrapsErr := fmt.Errorf("... %w ...", ..., err, ...)
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//
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// Successive unwrapping of an error creates a tree. The [Is] and [As]
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// functions inspect an error's tree by examining first the error
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// itself followed by the tree of each of its children in turn
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// (pre-order, depth-first traversal).
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//
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// [Is] examines the tree of its first argument looking for an error that
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// matches the second. It reports whether it finds a match. It should be
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// used in preference to simple equality checks:
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//
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// if errors.Is(err, fs.ErrExist)
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//
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// is preferable to
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//
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// if err == fs.ErrExist
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//
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// because the former will succeed if err wraps [io/fs.ErrExist].
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//
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// [As] examines the tree of its first argument looking for an error that can be
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// assigned to its second argument, which must be a pointer. If it succeeds, it
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// performs the assignment and returns true. Otherwise, it returns false. The form
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//
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// var perr *fs.PathError
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// if errors.As(err, &perr) {
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// fmt.Println(perr.Path)
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// }
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//
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// is preferable to
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//
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// if perr, ok := err.(*fs.PathError); ok {
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// fmt.Println(perr.Path)
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// }
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//
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// because the former will succeed if err wraps an [*io/fs.PathError].
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package errors
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// New returns an error that formats as the given text.
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// Each call to New returns a distinct error value even if the text is identical.
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func New(text string) error {
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return &errorString{text}
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}
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// errorString is a trivial implementation of error.
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type errorString struct {
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s string
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}
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func (e *errorString) Error() string {
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return e.s
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}
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// ErrUnsupported indicates that a requested operation cannot be performed,
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// because it is unsupported. For example, a call to [os.Link] when using a
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// file system that does not support hard links.
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//
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// Functions and methods should not return this error but should instead
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// return an error including appropriate context that satisfies
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//
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// errors.Is(err, errors.ErrUnsupported)
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//
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// either by directly wrapping ErrUnsupported or by implementing an [Is] method.
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//
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// Functions and methods should document the cases in which an error
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// wrapping this will be returned.
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var ErrUnsupported = New("unsupported operation")
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