> For clean Markdown content of this page, append .md to this URL. For the complete documentation index, see https://buildwithfern.com/learn/llms.txt.

## 0.35.0

**`(feat):`** Add runtime validation for discriminated unions to prevent users from accidentally sending the wrong type of value. With this, users will be expected to set exactly one of the union's values like so:

**`package example`**

````go package example
type Animal struct {
  Type string
  Cat  *Cat
  Dog  *Dog
}
func do() {
  union := &Animal{
    Cat: &Cat{
      Name: "Fluffy",
    },
  }
} ```
If the user sets _both_ `Cat` and `Dog`, the user will receive an error when the type is serialized to JSON (i.e. in the `json.Marshaler` implementation).

## 0.34.0
**`(feat):`** Add support for sending the `User-Agent` header on every request. Go packages are uniquely identified by their full module path, so the `User-Agent` header is generated in the `<module>/<version>` format, e.g.
``` User-Agent: github.com/acme/acme-go/1.0.0 ```

````