In Go, Given an interface{} in which I know what interface it implements, how can I convert to it -

my current problem implementing data-structures , have written iterators them. have visible interfaces data-structures, iterators, , other required objects. in have concrete implementations wish hide end user.

this requires many of functions return interface{} objects can store type of object (and leave validation end-user).

one problem have iterate on graph. iterator{} graph implementation returns concrete vertex type iterator interface returns interface{}. since end-users can base vertex interface have try convert vertex interface can use it.

here smallest example think of @ point illustrates issue:

package main  import (     "fmt"     "strconv" )  type base interface {     required() string }  type concrete struct {     _data int } func (con *concrete) required() string {     return strconv.itoa(con._data) }  func convert(val interface{}) *base {     if con,ok := val.(*base); ok {         return con     }     return nil }  func main() {     conc := new(concrete)     conc._data = 5      base := convert(conc)      fmt.println(base) } 

in code above wish convert convert type *base. function convert return value nil instead of lovely value wish be.

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edit: removed unused code, thought had removed guess not.

now have finished writing long explanation had idea , figured out solution:

func convert(val interface{}) base {     if con,ok := val.(base); ok {         return con     }     return nil } 

don't try cast pointer rather base interface.

i not sure why case. when reflect.typeof(val) inside of convert gives output

*main.concrete 

i hope other people find useful , else can answer why portion of answer.