How to type cast a child struct to parent type to pass to a func

[prajakta....@gmail.com]

I am trying to pass the parent struct type to a method

package main

import "fmt"

type Child struct  {

     Parent  //embed

     Attr string

}

type Parent struct {

    Attr1 string

}

func setf(p Parent) {

fmt.Println(p)   

}

func main() {

var ch Child

    ch.Attr = "1"

    ch.Attr1 = "2"

    setf(ch) // This does not work - cannot use ch (type Child) as type Parent in argument to setf

}

How do I resolve this problem?

[Andrew Gerrand]

Hi,

When you embed the "Parent" struct inside the "Child" struct, the Parent struct is visible as a field named "Parent" of the Child struct.

http://play.golang.org/p/TDY10AMS2d

So in your code, you should be able to write:

  setf(ch.Parent)

Hope this helps,

Andrew

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[prajakta....@gmail.com]

Hello Andrew

I want to do something else. I want to type cast the Child with Parent. So that I can have a generic method which accepts any object of any of the child structs which are inherited from parent. 

So if I have child1 child2 structs derived from parent. I will write a common method like setf(p Parent)  which can accept any child type object as parameter.

[bcgr...@gmail.com]

Is the below along the lines you're looking for? playground link 

package main

import "fmt"

type Parent struct {

Attr1 string

}

type Parenter interface {

GetParent() Parent

}

type Child struct {

Parent //embed

Attr   string

}

func (c Child) GetParent() Parent {

return c.Parent

}

func setf(p Parenter) {

fmt.Println(p)

}

func main() {

var ch Child

ch.Attr = "1"

ch.Attr1 = "2"

setf(ch)

}

[parais...@gmail.com]

There is no typecasting or inheritance in Go. Go doesn't support covariance or contra variance and its type system has no hierarchy for named types.

Write an interface and set "setf" argument type as that interface.It is the only way you'll get some polymorphism out of Go. whatever you are used to in other statically typed languages such as Java doesn't exist with Go type system.

[Prajakta Dandawate]

Thank you. Yes I am looking for somewhat similar. I am testing it.

Is this called as Type assertion method

[Prajakta Dandawate]

Ok. Thank you All.

So now if I have to add any method for Chile, should be also added to interface or only parent's methods are added to interface?

[Haddock]

Maybe this helps: http://objectscape.blogspot.de/2013/09/inner-pattern-to-mimic-method.html

[Egon]

On Tuesday, 23 June 2015 08:57:38 UTC+3, prajakta....@gmail.com wrote:

I am trying to pass the parent struct type to a method

Can you explain the actual problem, not the facilitated example, you are facing. Maybe there is a simpler/cleaner solution than using Child, Parent. If you can remove the cycle things might get significantly simpler.

+ Egon