Accessing nested functions and scope?

Okay, this would make my life a lot easier if this could be done somehow.
How can one class access a nested function in another class.

main class{
   public function main(){
   public function doSomethin(){
          function doSomethin2(){ //  <----Nested Function

//In a separate file
public function dostuff(){
     // <====== needs to call doSomethin2() from here somehow when it finished its dostuff!

public function

Also, thanks for putting up with my bombardment of stupid.