Immutable member functions on mutable objects

[Tomek Sowiñski]

I've got a problem calling an immutable getter on an "ordinary" object.

struct A {
    float _pole;
    float pole() immutable {
        return _pole;
    }
}

void main() {
    A a;
    auto x = a.pole;   // Ouch!
}

Error: function hello.A.pole () immutable is not callable using argument types 
()

There's no problem when pole is const. I assume the problem is the hidden 
"this" parameter (is it? the message is a bit confusing). Then again, A is 
implicitly convertible to immutable(A) so there shouldn't be a problem, no? 
Maybe a compiler bug?

BTW, can someone explain what's exactly the difference between a const and 
immutable member function? The D page says only about the latter.

Tomek