README.md
# generr
[](https://circleci.com/gh/akito0107/generr)
[](https://codeclimate.com/github/akito0107/generr/maintainability)[](https://codeclimate.com/github/akito0107/generr/test_coverage)
generate error utilities for golang.
Inspired by [BANZAI CLOUD's Error Handling Practices in Go](https://banzaicloud.com/blog/error-handling-go/),
this command generate custom error utilities from simple `interface` declaration.
## Getting Started
### Prerequisites
- Go 1.11+
- make
### Installing
```
$ go get -u github.com/akito0107/generr/cmd/generr
```
### How to use
1. You declare `interface` which must have a single function and *named* return values (if needs).
```go
type userNotFound interface {
UserNotFound() (id int64)
}
```
2. Generate implementation with passing the type name.
```sh
$ generr -t userNotFound
```
3. Then, you can get implementation file which named `userNotFound_check.go`.
This file contains the function which identifies whether given error is the one that we are defined before.
```go
func IsUserNotFound(err error) (bool, int64) {
var id int64
if e, ok := err.(userNotFound); ok {
id = e.UserNotFound()
return true, id
}
return false, id
}
```
4. You can also generate struct which implements `error` and the `interface` with `-i` option.
```sh
$ generr -t userNotFound -i -it userNotFound -o ../otherpackage
```
You get generated file named `userNotFound_impl.go`.
```go
package otherpackage
type userNotFound struct {
Id int64
}
func (e *userNotFound) UserNotFound() int64 {
return e.Id
}
func (e *userNotFound) Error() string {
return fmt.Sprintf("userNotFound Id: %v", e.Id)
}
```
You can pass struct name with `-it` option (default case is capitalized name given with `-t`).
`-o` option (default location is current directory and package).
5. You can unify `check` and `impl` files with `-u` option.
```sh
$ generr -t userNotFound -i -u
```
```go
func IsUserNotFound(err error) (bool, int64) {
var id int64
if e, ok := err.(userNotFound); ok {
id = e.UserNotFound()
return true, id
}
return false, id
}
type UserNotFound struct {
Id int64
}
func (e *UserNotFound) UserNotFound() int64 {
return e.Id
}
func (e *UserNotFound) Error() string {
return fmt.Sprintf("userNotFound Id: %v", e.Id)
}
```
6. You can also use `go generate`
```go
//go:generate generr -t notFound -i -u
type userNotFound interface {
UserNotFound() (id int64)
}
```
```sh
$ go generate // you can get same results.
```
6. You can pass custom error message with `-m` flag.
```go
//go:generate generr -t emailNotFound -m "email %s not found" -i -u
type emailNotFound interface{
EmailNotFound() (email string)
}
```
and run `go generate`
```sh
$ go generate
```
then, you get custom error utilities with passed error message.
```go
// Code generated by "generr"; DO NOT EDIT.
package e2e
import "fmt"
func IsEmailNotFound(err error) (bool, string) {
var email string
if e, ok := err.(emailNotFound); ok {
email = e.EmailNotFound()
return true, email
}
return false, email
}
type EmailNotFound struct {
Email string
}
func (e *EmailNotFound) EmailNotFound() string {
return e.Email
}
func (e *EmailNotFound) Error() string {
return fmt.Sprintf("email %s is not found", e.Email)
}
```
## Options
```sh
$ generr -h
NAME:
generr - generate custom error from interface
USAGE:
generr [OPTIONS]
VERSION:
0.0.0
COMMANDS:
help, h Shows a list of commands or help for one command
GLOBAL OPTIONS:
--type value, -t value error interface name (required)
--dryrun dryrun (default=false)
--implementation, -i generate error implementation (default=false)
--unify, -u (only affects with --implementation option) unify implementation with checking function (default=false)
--implementation-output-path value, -o value (only affects with --implementation option) implementation output path (default=current directory)
--implementation-type value, --it value (only affects with --implementation option) implementation type name (default=capitalized given type name)
--message value, -m value custom error message (optional)
--cause, -c append cause check (default=false)
--help, -h show help
--version, -v print the version
```
## License
This project is licensed under the Apache License 2.0 License - see the [LICENSE](LICENSE) file for details