On Wed, 16 Mar 2011 22:05:49 +0100, Steven Schveighoffer
<[email protected]> wrote:
On Wed, 16 Mar 2011 16:49:53 -0400, Simen kjaeraas
<[email protected]> wrote:
On Wed, 16 Mar 2011 16:23:47 +0100, Steven Schveighoffer
<[email protected]> wrote:
struct Point2 {
int x, y;
void draw(Canvas c) {...}
}
struct Point3 : Point2 {
int z;
void draw(Canvas c) {...}
}
Point3 p3;
Point2 *p2 = &p3;
// what does this do?
p2.draw(c);
Nothing. You should got a type error upon attempting to assign a p3* to
a p2*.
We are assuming struct inheritance works here, as in C++. In C++ I can
the address of a derived object to a base class pointer without a cast.
And I was assuming we tried to fix C++'s problems in that regard. If we
were to use the rule I chose, the slicing problem is moot.
This exact code compiles in C++ except for putting semi-colons after the
structs (BTW, I have to mention that I freaking LOVE D for eliminating
that)
I know. It's my number one C/C++ mistake, and same for all students I've
had to help (as well as some teachers :).
and change p2.draw(c) to p2->draw(c).
Even if you say that you shouldn't be allowed to do that, then you are
going to have complaints as to why it's different from C++...
We already have that. Just the other day, some guy named Jens complained
that D structs can't be derived from.
The point is, if we allow inheritance on structs, it causes more
confusion to people who expect certain things from inheritance than it
beautifies syntax.
I agree. I also prefer alias this, both for its flexibility and its
distinctiveness. I just felt that the slicing problem is trivially fixed,
and thus need not be a part of the discussion.
--
Simen
