Class inside a Struct?

[chardetm via Digitalmars-d-learn]

Hello everyone,

I am currently learning D by coding a project, but I encountered
a problem with one of my structures. I managed to reduce the code
to the minimum:




import std.stdio;
import std.container.rbtree;

struct Container {
        
        private RedBlackTree!int _rbtree = new RedBlackTree!int;

        void add (int elt) {
                _rbtree.insert(elt);
        }

        void print () {
                if (_rbtree.empty) {
                        writeln("empty");
                } else {
                        foreach (l; _rbtree) {
                                write(l, " ");
                        }
                        writeln();
                }
        }

}

int main () {
        Container c1, c2;
        c1.add(1);
        c1.print();
        c2.print();
        return 0;
}




I don't understand why the output of this program is:

1
1


I expect it to be:

1
empty


I thank you in advance for your help!