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Created ErrorValueFAQ (markdown)

Jonathan Amsterdam 2019-03-12 11:07:31 -04:00
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# Error Values: Frequently Asked Questions
The Go 2 [error values proposal](https://go.googlesource.com/proposal/+/master/design/29934-error-values.md) adds functionality to the [`errors`](https://tip.golang.org/pkg/errors) and [`fmt`](https://tip.golang.org/pkg/fmt) packages of the standard library for Go 1.13. There is also a compatibility package, [`golang.org/x/xerrors`](https://godoc.org/golang.org/x/xerrors), for earlier Go versions.
We suggest using the `xerrors` package for backwards compatibility. When you no longer wish to support Go versions before 1.13, use the corresponding standard library functions.
## How should I change my error-handling code for Go 1.13?
You need to be prepared that errors you get may be wrapped.
- If you currently compare errors using `==`, use `xerrors.Is` instead. Example:
```
if err == io.ErrUnexpectedEOF
```
becomes
```
if xerrors.Is(err, io.ErrUnexpectedEOF)
```
- Checks of the form `if err == nil` need not be changed.
- Comparisons to `io.EOF` need not be changed, because `io.EOF` should never be wrapped.