Re: Ada / C++ comparison paper

["Hyman Rosen" <hyrosen@mail.com>]

"Greg C" <gmc444@yahoo.com> wrote in message
news:62340e2a.0112190810.16f029ff@posting.google.com...
> Actually, this is not true. In Eiffel the parent's methods can declare
> parameter types such that child classes can be substituted.

"Can" but not "must". In C++ terms, Eiffel allows this:

struct a { virtual void f(const a &p_a) const; };
struct b : a { virtual void f(const b &p_b) const; };

with b::f considered the overrider of a::f. Now, suppose
I have this function:

void apply(const a &a1, const a &a2) { a1.f(a2); }

Even though this compiles without any problem, I have
no assurance that it will not fail at runtime, because it's
possible for a1 to refer to a "b" object while a2 refers
to an "a" object. Eiffel advocates hope for whole-program
analysis to save them from this by trying to track whether
such a case actually arises. Feh.