[go-nuts] Set a different value to the field of an interface's sctruct

I have added a function, "SetSalt", to an interface to can re-use the code
of other function:
   https://github.com/kless/crypt/blob/master/crypt.go#L42

What I do, is to get the md5_crypt, for then to set a different prefix:
   https://github.com/kless/crypt/blob/master/apr1_crypt/apr1_crypt.go#L28

where SetSalt in md5_crypt, sets the new values:
   https://github.com/kless/crypt/blob/master/md5_crypt/md5_crypt.go#L159

var md5Crypt = md5_crypt.New()


func init() {
  md5Crypt.SetSalt(&common.Salt{
   MagicPrefix: []byte(MagicPrefix),
  })
}


But when I set directly the entire struct, "c.Salt=salt", it is not copying
it like I was expecting, since the MagiPrefix follows being what was in md5:

func (c crypter) SetSalt(salt *common.Salt) {

  c.Salt = salt

}


The only way is set it thus:

c.Salt.MagicPrefix = salt.MagicPrefix


===

Now well, if I can set it the next code which is similar (with the exceptionofthe interface),
why is failling in upper code?

* * *
package main

import "fmt"

type foo struct {
     s string
     i int
}

type bar struct{ Foo *foo }

var foo1 = &foo{
     "b",
     500,
}

func main() {
     _bar := bar{
         &foo{
             "a",
             10,
         },
     }
     fmt.Println(_bar.Foo)

     _bar.Foo = foo1
     fmt.Println(_bar.Foo)
}
* * *
&{a 10}
&{b 500}