Passing a derived class where base class is defined as ref parameter

[chopchop]

Hi guys,

below a small piece of code, which does not compile because "b" 
of type B can not be passed as ref parameter to incr(ref A a).

If I remove the ref, it works as expected, that is to say I can 
give a derived class as parameter. I have an idea why it does not 
work, but I think a c++ reference would work, ie incr(A& console) 
would accept a B as parameter. What the logic here?

Thanks

```
void main()
{
     import std.stdio: write, writeln, writef, writefln;

     class A
     {
     	int i = 2;
     }

     class B : A
     {
     	int j= 3;
     }

     void incr(ref A a)
     {
     	writeln(a.i);
     }

     B b = new B();
     incr(b);

}
```