我正在检查Go v1.13 Go v1.14的错误跟踪。为什么只有不带参数或带值接收器的错误实现才可以用 errors.Is()
? 这意味着,一个能够封装的错误实现必须有一个值接收器,才能被发现与 errors.Is()
.
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.orgp-hSukZ-gii2。
编辑:看来,任何参数的差异,包括在包装错误参数。Err
,将导致无法找到该类型与 errors.Is()
.
你得到的原因是 false
试图在另一个错误中找到一个错误时,通过 errors.Is
是因为--虽然这两个错误可能有相同的字段值,但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
那么如何检测这种 "类型 "的错误呢?和 得其值 errors.As
而不是。
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)}
}