fmt.Print（myError）而不隐式调用Error（）？

Question

I want to print everything in my custom error struct like fmt.Print() prints any other struct, but since it implements error it only prints one field, the one I pass out through Error().

How can I do this?

Answer 1

You can type assert the error interface to your custom type. Note that you should, ideally, use the 'comma, ok' idiom when doing so otherwise your application will panic if the type assertion fails.

package main

import "fmt"

type MyError struct {
    Status  int
    Message string
}

func (e MyError) Error() string {
    return e.Message
}

func BadThing() error {
    return MyError{404, "Not found"}
}

func main() {
    err := BadThing()
    if err != nil {
        if v, ok := err.(MyError); ok {
            fmt.Printf("%+v
", v.Status) // or v, or v.Message, etc.
        }
        fmt.Printf("%v
", err) // Fallback. Can wrap in this in an 'else' if needed.
    }
}

Playground - and further reading: http://blog.golang.org/error-handling-and-go