We have a handy dandy syntax for this: if (MyClassInt subclass = cast(MyClassInt)value) { writeln(subclass.value); }If it doesn't cast to said type (it will be null) that branch won't execute.
Just out of interest: it looks like a dynamic_cast in C++ which is considered as slow operation. Is that D cast also a dynamic cast and also slow? I've never used it, so I'm a bit curious.
