go - How do I pass in an interface{} to a function as a specific structure? -

i trying have generic routine handle messages between specific components. part of involves reading byte array , using json.marshal , json.unmarshal , calling callback.

i trying pass interface function expects specific structure, not know type of target structure. in code below, how function r() call function cb() , pass in correct data?

package main  import (     "encoding/json"     "fmt"     "reflect" )  type bottom struct {     foo string }  func cb(b *bottom) {      fmt.println("5. ", b) }  func r(t interface{}, buf []byte) {      _ = json.unmarshal(buf, &t)      fmt.println("2. ", reflect.typeof(t))     fmt.println("3. ", t)      cb(&t) }  func main() {     x := bottom{foo: "blah"}     var y bottom      buf, _ := json.marshal(x)      fmt.println("1. ", x)     r(&y, buf) } 

you need use type assertion convert interface{} type function requires. can add error checking appropriately handle case parameter can't typecast desired type.

see generic playground demonstrates solution: http://play.golang.org/p/nyeoavteea

in case, means

cb(&t.(bottom)) 

you can add error checking:

bottom, ok := t.(bottom) if !ok {   // } cb(&bottom)