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.