type Person struct {
    Name       string
    MiddleName *string
    Surname    string
}
type User struct {
    Person
    Email   string
    Age     int8
    Married bool
}
type Employee struct {
    Name       string
    MiddleName string
    Surname    string
    Email      string
    Age        int
}
src := User{
    Person: Person{
        Name:       "John",
        MiddleName: nil,
        Surname:    "Smith",
    },
    Email:   "john.smith@joy.me",
    Age:     33,
    Married: false,
}
dst := Employee{}
copiers := copy.New() // New("json")
copiers.Copy(&dst, &src)
// Or more fast use case is to create the type specific copier.
copier := copiers.Get(&Employee{}, &User{}) // Created once for a pair of types.
copier.Copy(&dst, &src)