This program shows the current default printing of class instances (dmd 2.067alpha):


class Foo {}
void main() {
    import std.stdio;
    Foo f;
    f.writeln;
    f = new Foo;
    writeln(f, " ", cast(void*)f);
}


Output:

null
test.Foo 2001FE0


But perhaps it's better for D writeln to print class instances (that don't have a toString) more like Java:

test.Foo@null
test.Foo@2001FE0 2001FE0


This is useful in debugging and code development, because the address allows to see what class instances are equal.