我正在检查Go v1.13 Go v1.14中的错误跟踪。为什么看来errors.Is()
只能找到没有参数或带有值接收器的错误实现?这意味着能够包装的错误实现必须具有一个值接收器,才能被errors.Is()
找到。
package main
import (
"fmt"
"errors"
)
type someAtomicError struct {}
func (e *someAtomicError) Error() string { return "Hi!" }
func checkAtomicError() {
e := &someAtomicError{}
e2 := fmt.Errorf("whoa!: %w", e)
e2IsE := errors.Is(e2, &someAtomicError{})
fmt.Println("atomic error trace ---\t\t", e2, "\t\t--- is traceable: ", e2IsE)
}
type someWrapperError struct {
Msg string
Err error
}
func (e someWrapperError) Error() string { return fmt.Sprintf("%s: %v", e.Msg, e.Err) }
func (e someWrapperError) Unwrap() error { return e.Err }
func checkWrapperError() {
e := someWrapperError{"Hi!", nil}
e2 := fmt.Errorf("whoa!: %w", e)
e2IsE := errors.Is(e2, someWrapperError{"Hi!", nil})
fmt.Println("wrapper error trace ---\t\t", e2, "\t--- is traceable: ", e2IsE)
}
type somePointerWrapperError struct {
Msg string
Err error
}
func (e *somePointerWrapperError) Error() string { return fmt.Sprintf("%s: %v", e.Msg, e.Err) }
func (e *somePointerWrapperError) Unwrap() error { return e.Err }
func checkPointerWrapperError() {
e := &somePointerWrapperError{"Hi!", nil}
e2 := fmt.Errorf("whoa!: %w", e)
e2IsE := errors.Is(e2, &somePointerWrapperError{"Hi!", nil})
fmt.Println("pointer wrapper error trace ---\t", e2, "\t--- is traceable: ", e2IsE)
}
func main() {
checkAtomicError()
checkWrapperError()
checkPointerWrapperError()
}
//atomic error trace --- whoa!: Hi! --- is traceable: true
//wrapper error trace --- whoa!: Hi!: <nil> --- is traceable: true
//pointer wrapper error trace --- whoa!: Hi!: <nil> --- is traceable: false
https://play.golang.org/p/-hSukZ-gii2
编辑:似乎参数上的任何差异(包括包装的错误参数Err
中的差异)都将导致无法使用errors.Is()
找到类型。
答案 0 :(得分:1)
尝试通过false
在另一个错误中查找一个错误时得到errors.Is
的原因是-尽管两个错误可能具有相同的字段值-它们是两个不同的内存指针:>
e := &somePointerWrapperError{"Hi!", nil}
ew := fmt.Errorf("whoa!: %w", e)
e2 := &somePointerWrapperError{"Hi!", nil} // e2 != e
errors.Is(ew, e2) // false - because `ew` wraps `e` not `e2`
errors.Is(ew, e) // true
因此,如何检测错误的这种“类型”并获得其值:请改用errors.As
:
e := &somePointerWrapperError{"Hi!", nil}
e2 := fmt.Errorf("whoa!: %w", e)
var ev *somePointerWrapperError
if errors.As(e2, &ev) {
fmt.Printf("%#v\n", ev) // &somePointerWrapperError{Msg:"Hi!", Err:error(nil)}
}
答案 1 :(得分:1)
远程相关,但可能对某人有所帮助:我花了一些时间才意识到 <CollectionView
x:Name="CollectionEditIcon"
Margin="10,5,10,5"
HorizontalOptions="Center"
SelectionMode="None">
<CollectionView.ItemsLayout>
<GridItemsLayout Orientation="Vertical" Span="1" VerticalItemSpacing="5" HorizontalItemSpacing="5"/>
</CollectionView.ItemsLayout> <CollectionView.ItemTemplate>
<DataTemplate>
<Grid>
<Entry x:Name="EntryEdit" Text="{Binding id}" TextColor="Black" FontSize="16" MaxLength="25" TextChanged="Entry_TextChanged" IsReadOnly="{Binding Edit}" Unfocused="EntryEdit_Unfocused"/>
实际上期望指向目标的双指针,而 errors.As(...)
则没有:
errors.Is(...)