On Thu, 27 May 2010 17:47:20 -0400, bearophile <bearophileh...@lycos.com>
wrote:
Steven Schveighoffer:
I have hoped that at some point, structs can be auto-composed,
without a vtable, but you still have to do this manually.
I don't understand what you mean here :-)
I mean simple inheritance. In C, there has always been manual
inheritance. You can see it with the sockaddr system, and even with the X
toolkit widget system.
essentially, when you derive type B from type A in C++, you get this:
struct B
{
A _a;
}
A is always put first, that way, a pointer to a B can always be used as a
pointer to an A.
The other thing that happens is that function calls on B also use A as
well. This is not so easy in C, but in D it is currently quite trivial:
struct B
{
A _a;
alias _a this;
}
Then a call like b.methodOfA(); gets translated statically to
b._a.methodOfA().
But there are things I don't like about this, such as you can *set* _a.
To get around that, you define a property getter, but not a setter:
struct B
{
private A _a;
@property ref A a() {return _a;}
alias a this;
}
What I would like is a common-sense approach to inheritance for structs
that just does not allow virtual methods or interfaces, and which does not
cast implicitly to the base (explicit cast is OK). I think some designs
would benefit greatly from this simple feature. I think it's more tricky
than I've described, but I think with some diligence it can be done.
-Steve
