generic.go

package main

import (
	"errors"
	"fmt"
)

// Person is a demo struct
type Person struct {
	Name string
}

// UnwrapPersonError accepts an interface and an error and returns a Person and an error
func UnwrapPersonError(i interface{}, err error) (Person, error) {
	if err != nil {
		return Person{}, err
	}

	p, ok := i.(Person)
	if !ok {
		return Person{}, errors.New("the given interface is not an Person")
	}
	return p, nil
}

// UnwrapPerson accepts an interface and returns a Person and an error
func UnwrapPerson(i interface{}) (Person, error) {
	return UnwrapPersonError(i, nil)
}

func main() {
	p, err := UnwrapPerson(func() interface{} {
		return Person{
			Name: "Claudemiro",
		}
	}())
	if err != nil {
		panic(err)
	}

	fmt.Println(p)
}