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// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package errors
import (
"reflect"
)
// An Wrapper provides context around another error.
type Wrapper interface {
// Unwrap returns the next error in the error chain.
// If there is no next error, Unwrap returns nil.
Unwrap() error
}
// Opaque returns an error with the same error formatting as err
// but that does not match err and cannot be unwrapped.
func Opaque(err error) error {
return noWrapper{err}
}
type noWrapper struct {
error
}
func (e noWrapper) FormatError(p Printer) (next error) {
if f, ok := e.error.(Formatter); ok {
return f.FormatError(p)
}
p.Print(e.error)
return nil
}
// Unwrap returns the next error in err's chain.
// If there is no next error, Unwrap returns nil.
func Unwrap(err error) error {
u, ok := err.(Wrapper)
if !ok {
return nil
}
return u.Unwrap()
}
// Is returns true if any error in err's chain matches target.
//
// An error is considered to match a target if it is equal to that target or if
// it implements an Is method such that Is(target) returns true.
func Is(err, target error) bool {
if target == nil {
return err == target
}
for {
if err == target {
return true
}
if x, ok := err.(interface{ Is(error) bool }); ok && x.Is(target) {
return true
}
// TODO: consider supporing target.Is(err). This would allow
// user-definable predicates, but also may allow for coping with sloppy
// APIs, thereby making it easier to get away with them.
if err = Unwrap(err); err == nil {
return false
}
}
}
// As finds the first error in err's chain that matches a type to which target
// points, and if so, sets the target to its value and reports success. An error
// matches a type if it is of the same type, or if it has an As method such that
// As(target) returns true. As will panic if target is nil or not a pointer.
//
// The As method should set the target to its value and report success if err
// matches the type to which target points and report success.
func As(err error, target interface{}) bool {
if target == nil {
panic("errors: target cannot be nil")
}
typ := reflect.TypeOf(target)
if typ.Kind() != reflect.Ptr {
panic("errors: target must be a pointer")
}
targetType := typ.Elem()
for {
if reflect.TypeOf(err) == targetType {
reflect.ValueOf(target).Elem().Set(reflect.ValueOf(err))
return true
}
if x, ok := err.(interface{ As(interface{}) bool }); ok && x.As(target) {
return true
}
if err = Unwrap(err); err == nil {
return false
}
}
}
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