[Issue 4251] Hole in the const system: immutable values can be overwritten (const(T) is appendable to const(T)[])

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=4251



--- Comment #18 from Steven Schveighoffer <schveiguy at yahoo.com> 2011-11-18 07:10:20 PST ---
(In reply to comment #17)
> (In reply to comment #16)
> >     B x;
> >     A* y=&x; // bad!
> Everything you describe is supposed to happen. "A* y = &x" is the point of
> inheritance. What exactly is the problem you see in the above? All of your
> assert elements seem fine too…

The example isn't illustrative enough.

Here's a better example:

class A {}
class B : A {void foo() {writeln("hello, B");} }

void main()
{
   B x;
   A* y = &x;
   *y = new A;
   x.foo(); // boom!  Call to invalid vtable entry
}

As I said in an earlier comment, this bug is really a dup of bug 2095, but it
adds a different twist.  If we want to consolidate, we should close this as a
duplicate of 2095.

> Reverting title. This bug is about the const safety design of the language, not
> about inheritance. Even if there is a problem with inheritance, it should be a
> separate bug unless you can argue they have the same cause.

It's somewhat the same thing.  const(T) is really a "base class" of T, since T
implicitly casts to const(T), but const(T) doesn't implicitly cast to T.

I won't revert the bug description again, because I think this case is already
covered in 2095.

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