Assign struct with another struct

Question

I have a RegistrationRequest struct:

type RegistrationRequest struct {
    Email    *string
    Email2   *string        
    Username *string
    Password *string
    Name     string
}

Where Email2 is the email value entered again to verify that what the user entered is correct.

I also have a User struct:

type User struct {
    Email    *string
    Username *string
    Password *string
    Name     string           
}

Of course, there is no need to store Email2 beyond registration.

So I have two variables: req and u - one for each struct. Is it possible to assign the req struct into to the u struct so that all the common fields will exist in the u struct?

Answer 1

Using simple assignment you can't because even though the fields of User are a subset of RegistrationRequest, they are completely 2 different types, and Assignability rules don't apply.

You could write a function which uses reflection (reflect package), and would copy all the fields from req to u, but that is just ugly (and inefficient).

Best would be to refactor your types, and RegistrationRequest could embed User.

Doing so if you have a value of type RegistrationRequest that means you already also have a value of User:

type User struct {
    Email    *string
    Username *string
    Password *string
    Name     string
}

type RegistrationRequest struct {
    User  // Embedding User type
    Email2 *string
}

func main() {
    req := RegistrationRequest{}
    s := "[email protected]"
    req.Email = &s

    s2 := "testuser"
    req.Username = &s2

    u := User{}
    u = req.User
    fmt.Println(*u.Username, *u.Email)
}

Output: (try it on the Go Playground)

testuser [email protected]

Also please note that since your structs contain pointers, when copying a struct, pointer values will be copied and not pointed values. I'm not sure why you need pointers here, would be best to just declare all fields to be non-pointers.

Also note that embedding is not really a requirement, it just makes your types and their usage more smooth. User could just as well be an "ordinary" field of RequistrationRequest, e.g.:

type RegistrationRequest struct {
    Usr User // This is just an ordinary field, not embedding
    Email2 *string
}