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# errdata
[](https://godoc.org/github.com/zeebo/errs/errdata)
[](https://sourcegraph.com/github.com/zeebo/errs?badge)
[](https://goreportcard.com/report/github.com/zeebo/errs/errdata)
errdata helps with associating some data to error classes.
### Adding data
The [Set][Set] function associates some data with some error class and key. For
example:
```go
var (
Unauthorized = errs.Class("unauthorized")
NotFound = errs.Class("not found")
)
type httpErrorCodeKey struct{}
func init() {
errdata.Set(Unauthorized, httpErrorCodeKey{}, http.StatusUnauthorized)
errdata.Set(NotFound, httpErrorCodeKey{}, http.StatusNotFound)
}
```
Why do that? [Get][Get] can read the associated data for an error if it was
wrapped by any of the Classes you have set data on. For example:
```go
func getStatusCode(err error) int {
code, _ := errdata.Get(err, httpErrorCodeKey{}).(int)
if code == 0 {
code = http.StatusInternalServerError
}
return code
}
```
If the error has been wrapped by multiple classes for that key, the value for
the most recently wrapped class is returned. For example:
```go
func whatStatusCodeCode() {
err := NotFound.Wrap(Unauthorized.New("test"))
fmt.Println(getStatusCode(err))
// output:
// 404
}
```
### Contributing
errdata is released under an MIT License. If you want to contribute, be sure to
add yourself to the list in AUTHORS.
[Set]: https://godoc.org/github.com/zeebo/errs/errdata#Set
[Get]: https://godoc.org/github.com/zeebo/errs/errdata#Get
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