accessing struct fields from embedded struct

Question

I want to define a method on a struct for validating http request. but I have some problems about accessing struct fields.

there is my code.

package main

import "log"

type ReqAbstract struct{}

func (r *ReqAbstract) Validate() error {
    log.Printf("%+v", r)
    return nil
}
func (r *ReqAbstract) Validate2(req interface{}) error {
    log.Printf("%+v", req)
    return nil
}

type NewPostReq struct {
    ReqAbstract
    Title string
}

func main() {
    request := &NewPostReq{Title: "Example Title"}

    request.Validate()
    request.Validate2(request)
}

When I run this code, I get the below result

2015/07/21 13:59:50 &{}
2015/07/21 13:59:50 &{ReqAbstract:{} Title:Example Title}

is there any way to access struct fields on Validate() method like Validate2() method?

Answer 1

You cannot access outer struct fields from inner struct. Only inner fields from the outer. What you can do is composing:

type CommonThing struct {
    A int
    B string
}

func (ct CommonThing) Valid() bool {
    return ct.A != 0 && ct.B != ""
}

type TheThing struct {
    CommonThing
    C float64
}

func (tt TheThing) Valid() bool {
    return tt.CommonThing.Valid() && tt.C != 0
}

Answer 2

You can define filed with point to himself

package main

import (
    "log"
)

type ReqAbstract struct{
    selfPointer interface{}
}

func (r *ReqAbstract) Assign(i interface{}) {
    r.selfPointer = i
}

func (r *ReqAbstract) Validate() error {
    log.Printf("%+v", r.selfPointer)
    return nil
}
func (r *ReqAbstract) Validate2(req interface{}) error {
    log.Printf("%+v", req)
    return nil
}

type PostReq struct {
    ReqAbstract
    Title string
}

func NewPostReq(title string) *PostReq {
    pr := &PostReq{Title:title}
    pr.Assign(pr)
    return pr
}

func main() {
    request := NewPostReq("Example Title")

    request.Validate()
    request.Validate2(request)
}

This will output:

2009/11/10 23:00:00 &{ReqAbstract:{selfPointer:0x10438180} Title:Example Title} 2009/11/10 23:00:00 &{ReqAbstract:{selfPointer:0x10438180} Title:Example Title}

Check playground