Golang: when typecasting child struct to parent struct, is child struct information lost?

Question

For example after embedding the parent struct in the child struct:

type ParentNode struct {
}

type ChildNode struct {
    ParentNode
    Ident string
}

func ParentType() ParentNode { 
    child := ChildNode{Ident : "node"}
    fmt.Println(child)
    return child.ParentNode 
}

func main() {
    x := ParentType()
    fmt.Println(x.Ident)

}

Would this print out "node" and also return the child struct wrapped in the parent struct with all the information, such that we can manipulate the apparent parent struct while having the actual child struct? The idea for this is similar to Java where you can return an apparent type of List but return an actual type of LinkedList.

If not, what would be the best way to achieve this functionality? Essentially I want to upcast the Child struct to a parent struct but manipulate it as if it was a child struct. Is there a way of solving this using an interface?

How is it possible to get rid of error "x.Ident undefined (type ParentNode has no field or method Ident)" at line fmt.Println(x.Ident)

W. Cybriwsky · Accepted Answer · 2015-11-15 06:05:38Z

2

It would not return the child struct. What you are doing is not typecasting the child struct, but just returning one of its fields. To use a more concrete example, the above go snippet would be like trying to use the name of an Employee as if it were a super class of Employee.

Your guess was right, though, that the way to achieve the "is-a" relationship like ArrayList and List is to use an interface. Know, though, that interfaces can only provide polymorphism for method calls, not field access. A modified version of your example, which is hopefully helpful, can be found at:

http://play.golang.org/p/qclS5KR64H

You would likely find it helpful to read the "Struct Types" portion of the go spec, and/or the whole spec (it's not that long! Or scary!):

https://golang.org/ref/spec#Struct_types

answered Nov 15, 2015 at 6:05

W. Cybriwsky

5813 silver badges6 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Golang: when typecasting child struct to parent struct, is child struct information lost?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related