The following code:

    import std.format, std.stdio;

    class X {
	mixin(members());
    }

    string members() {
	import std.container.rbtree;
   	auto rbt = redBlackTree(3, 1, 4, 2, 5);
	int x = rbt.front;
	return format("int y = %s;\n", x);
    }

fails to work at compile time with the message "cannot cast ... to ... at compile time".