TypeInfo madness

[Yuxuan Shui via Digitalmars-d]

In D (tested with D 2.070), one is allowed to modify TypeInfo 
returned by typeid().

Here is an example how this "feature" can be used maliciously.
        class A{
        }
        class C : A{
                int a = 1234;
        }
        class B : A{
                float b;
        }

        @safe void main() {
                import std.stdio;
                C c = new C;
                A a = cast(A)c;
                auto y = typeid(c);

                B b = new B;
                y.base = typeid(b);

                b = cast(B)a;
                assert(b !is null);
                writeln(b.b);
        }

With a successful dynamic cast, it should be safe to assume the 
data in the result object is well formed (enforced, for example, 
by invariants). However, the ability to modify a TypeInfo object 
will give the attacker a chance to pass crafted data to a 
function.