Proposal: try function constructor

Li

unread,

Jun 28, 2019, 10:49:55 PM6/28/19

to golang-nuts

I propose a addition to current try proposal to enable optional error wrapping.

demo codes:

package main

import (
	"fmt"
	"io"
	"os"
)

// wrapErr is an error wrapping function
func wrapErr(err error, format string, args ...interface{}) error {
	return fmt.Errorf(
		"%s: %s",
		fmt.Sprintf(format, args...),
		err.Error(),
	)
	// or other error implementation
}

// like the proposed try function but with custom wrapper
var try = makeTry(wrapErr)

// use like the proposed try with extra wrapping arguments
func CopyFile(src, dest string) (err error) {
	r := try(os.Open(src), "open %s", src)
	// if there is an error, it will be "open <src>: <err>" as returned by wrapErr
	defer r.Close()
	w := try(os.Create(dest), "create %s", dest)
	defer func() {
		w.Close()
		if err != nil {
			os.Remove(dest)
		}
	}()
	try(io.Copy(w, r)) // bare try without arguments, so no wrapping
	try(w.Close())
	return nil
}

Actually I have implemented this by abusing panic/recover.

Implementation: https://github.com/reusee/e/blob/master/error.go#L16

Example: https://github.com/reusee/e/blob/master/example_test.go#L15

I've been using this for a while. It works well to serve its purpose although bring in a little more overhead of panic/recover.

Denis Cheremisov

unread,

Jun 29, 2019, 3:22:41 PM6/29/19

to golang-nuts

Pooof

Are you serious?

Li

unread,

Jun 29, 2019, 8:14:30 PM6/29/19

to golang-nuts

Here's another demo that annotate errors with custom type.

package main

import (
	"fmt"
	"io"
	"os"
)

type Err struct {
	Code    string
	Message string
	Cause   error
}

var _ error = Err{}

func (e Err) Error() string {
	return fmt.Sprintf("[%s] %s: %s", e.Code, e.Message, e.Cause.Error())
}

// wrapErr annotates an error with code and message
func wrapErr(err error, code string, message string, args ...interface{}) error {
	return Err{
		Code:    code,
		Message: fmt.Sprintf(message, args...),
		Cause:   err,

	}
}

// like the proposed try function but with custom wrapper
var try = makeTry(wrapErr)

// use like the proposed try with extra wrapping arguments
func CopyFile(src, dest string) (err error) {

	r := try(os.Open(src), "Open", "open %s", src)
	defer r.Close()
	w := try(os.Create(dest), "Create", "create %s", dest)

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