Can't pass private symbols as alias parameter

[deadalnix via Digitalmars-d]

module a;

struct A(alias foo) {
     auto foo() {
         return foo();
     }
}

module b;

import a;

void main() {
     auto a = A!bar();
}

private int bar() { return 42; }

This do not work. I think it is a bug but I see how could see it 
as a feature. Which one is it ?