- In [cenkalti/backoff](https://github.com/cenkalti/backoff), it is implemented using a [`PermanentError`](https://pkg.go.dev/github.com/cenkalti/backoff/v4#Permanent) type. - In [avast/retry-go](https://github.com/avast/retry-go), it is implemented using the [`RetryIf`](https://pkg.go.dev/github.com/avast/retry-go#RetryIf) function and the [`Unrecoverable`](https://pkg.go.dev/github.com/avast/retry-go#Unrecoverable) type.
PermanentErrortype.RetryIffunction and theUnrecoverabletype.