这是我参与「第五届青训营 」伴学笔记创作活动的第 3 天
引入
在Go语言中，Error和Panic都表示“错误”，但它们之间的严重程度却有所不同。
Error举例
以下案例选自Go官方文档。
// In Go it's idiomatic to communicate errors via an
// explicit, separate return value. This contrasts with
// the exceptions used in languages like Java and Ruby and
// the overloaded single result / error value sometimes
// used in C. Go's approach makes it easy to see which
// functions return errors and to handle them using the
// same language constructs employed for any other,
// non-error tasks.
package main
import (
"errors"
"fmt"
)
// By convention, errors are the last return value and
// have type `error`, a built-in interface.
func f1(arg int) (int, error) {
if arg == 42 {
// `errors.New` constructs a basic `error` value
// with the given error message.
return -1, errors.New("can't work with 42")
}
// A `nil` value in the error position indicates that
// there was no error.
return arg + 3, nil
}
// It's possible to use custom types as `error`s by
// implementing the `Error()` method on them. Here's a
// variant on the example above that uses a custom type
// to explicitly represent an argument error.
type argError struct {
arg int
prob string
}
func (e *argError) Error() string {
return fmt.Sprintf("%d - %s", e.arg, e.prob)
}
func f2(arg int) (int, error) {
if arg == 42 {
// In this case we use `&argError` syntax to build
// a new struct, supplying values for the two
// fields `arg` and `prob`.
return -1, &argError{arg, "can't work with it"}
}
return arg + 3, nil
}
func main() {
// The two loops below test out each of our
// error-returning functions. Note that the use of an
// inline error check on the `if` line is a common
// idiom in Go code.
for _, i := range []int{7, 42} {
if r, e := f1(i); e != nil {
fmt.Println("f1 failed:", e)
} else {
fmt.Println("f1 worked:", r)
}
}
for _, i := range []int{7, 42} {
if r, e := f2(i); e != nil {
fmt.Println("f2 failed:", e)
} else {
fmt.Println("f2 worked:", r)
}
}
// If you want to programmatically use the data in
// a custom error, you'll need to get the error as an
// instance of the custom error type via type
// assertion.
_, e := f2(42)
if ae, ok := e.(*argError); ok {
fmt.Println(ae.arg)
fmt.Println(ae.prob)
}
}
在这段代码中，我们使用了error.New()函数创建了一个错误，类似于Java中的new Exception()，不过，它们的处理方法有所不同。
如果要将它们抛出去该怎么做呢？
在Java中，我们需要使用throw关键字将一个Expection对象丢给父级处理。而在Go语言中，则是使用返回值的形式告知外界产生了错误，外界可以接受这个错误进行处理，也可以使用_这一符号将其忽略，相比之下，Go的实现更加简洁。
Error举例
以下案例选自Go官方文档。
// A `panic` typically means something went unexpectedly
// wrong. Mostly we use it to fail fast on errors that
// shouldn't occur during normal operation, or that we
// aren't prepared to handle gracefully.
package main
import "os"
func main() {
// We'll use panic throughout this site to check for
// unexpected errors. This is the only program on the
// site designed to panic.
panic("a problem")
// A common use of panic is to abort if a function
// returns an error value that we don't know how to
// (or want to) handle. Here's an example of
// `panic`king if we get an unexpected error when creating a new file.
_, err := os.Create("/tmp/file")
if err != nil {
panic(err)
}
}
在本地开发环境下，有如下提示：
可以发现，Create()函数被提示为“不可达的”，Panic()让程序停了下来，它的严重程度明显高于Error。
Go官方文档指出，建议使用Error去替代Panic，只有当不知道如何处理这个错误或者不想处理这个错误的时候，才去使用Panic。
总结
panic用于真正异常的情况error的严重程度低于panic- 开发过程中应尽量使用
error而不是panic
