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xerrors.go
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xerrors.go
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// +build !js
// Copyright (c) 2019 The Go Authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
package oops
import "reflect"
// A 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
}
// Unwrap returns the result of calling the Unwrap method on err, if err implements
// Unwrap. Otherwise, Unwrap returns nil.
func Unwrap(err error) error {
u, ok := err.(Wrapper)
if !ok {
return nil
}
return u.Unwrap()
}
// Is reports whether 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 a method Is(error) bool 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
}
if err = Unwrap(err); err == nil {
return false
}
}
}
// As finds the first error in err's chain that matches the type to which target
// points, and if so, sets the target to its value and returns true. An error
// matches a type if it is assignable to the target type, or if it has a method
// As(interface{}) bool such that As(target) returns true. As will panic if target
// is not a non-nil pointer to a type which implements error or is of interface type.
//
// The As method should set the target to its value and return true if err
// matches the type to which target points.
func As(err error, target interface{}) bool {
if target == nil {
panic("errors: target cannot be nil")
}
val := reflect.ValueOf(target)
typ := val.Type()
if typ.Kind() != reflect.Ptr || val.IsNil() {
panic("errors: target must be a non-nil pointer")
}
if e := typ.Elem(); e.Kind() != reflect.Interface && !e.Implements(errorType) {
panic("errors: *target must be interface or implement error")
}
targetType := typ.Elem()
for err != nil {
if reflect.TypeOf(err).AssignableTo(targetType) {
val.Elem().Set(reflect.ValueOf(err))
return true
}
if x, ok := err.(interface{ As(interface{}) bool }); ok && x.As(target) {
return true
}
err = Unwrap(err)
}
return false
}
var errorType = reflect.TypeOf((*error)(nil)).Elem()