Rationale for classes as reference types

[A Lahav]

Steven Schveighoffer Wrote:

> "Bill Baxter" wrote
> > On Fri, Aug 8, 2008 at 1:10 AM, Steven Schveighoffer
> > wrote:
> >> "A Lahav" wrote
> >>> Can anyone please explain the design rationale for classes being 
> >>> reference
> >>> types exclusively?
> >>>
> >>> I ask this because I really like my classes to be allocated on the stack
> >>> or be value-type data members, the performance boost you get eliminiting
> >>> all these unnecessary heap operations is entirely not neglible.
> >>>
> >>> Otherwise I'll have a real problem considering D for my own use...
> >>
> >> Because of many reasons Walter has described in the past.  The one that
> >> sticks out to me is the chopping effect (don't know if this is the right
> >> term).  Let's say a function returns a non-reference class instance, and
> >> your function returns a derived instance.  The return value chops off the
> >> derived stuff.
> >
> > It's called "slicing".

Thanks - so where can I find what Walter said?

> >
> >> I like the way classes are always references.  But there is a way to 
> >> ensure
> >> a class gets allocated on the stack:
> >>
> >> scope c = new MyClass(...);
> >>
> >> This will allocate the class on the stack.  Be sure not to return a
> >> reference to it later though!
> >>
> >> Another possibility is to use structs instead, which do not have
> >> inheritance, and so will not cause the chopping effect.
> >
> > As has been mentioned in the past, it would definitely be nice if you
> > could also make a "scope MyClass" as a member of another class or
> > struct.
> 
> I also would like this request to be granted: 
> http://d.puremagic.com/issues/show_bug.cgi?id=2070
> 
Agree, and more than that - why shouldn't it be the default case?

> -Steve 
> 
> 

Another thing I didn't find any information about, I guess you know more than me here:
My dream is having member classes size determined in (dynamic) link time. This would solve IMHO a lot of versioning problems without having to revert to heap-allocated objects and object factories. Probably such a request entails an ABI modification. Can anyone comment?