Developing a plan for D2.0: Getting everything on the table

[Brad Roberts]

On Mon, 27 Jul 2009, Andrei Alexandrescu wrote:

> Bill Baxter wrote:
> > The requirement to add the post-blit is a little annoying.  If a
> > ValueContainer is made fundamental and it is built initially out of
> > components with value semantics, then no explicit post-blit will be
> > necessary.  However if you go the other way and start with a
> > RefContainer then a post-blit will be necessary when you implement the
> > ValueContainer based on it.   So to me it seems a little better to go
> > with the ValueContainer as the base implementation.
> 
> I think it's a matter of the most frequent use. I used to be a staunch
> supporter of values for containers, until Walter revealed to me that in STL
> you have value containers to constantly worry about adding the "&" everywhere.
> Implicitly copying containers is 95% of cases an error in C++ code. Witness
> all that advice about pass by reference etc. So why make that the default, one
> might ask? Better go with the flow and make the default case the easy case
> (reference), and if someone does want a value, have them write
> Value!Container.
> 
> 
> Andrei

There's two layers to talk about, the container itself and the elements it 
contains.  I agree that the container itself should be ref given the above 
logic (which matches my experience).  The less obvious one, imho, is the 
default of the contained.  Again, c++ uses value containership, but an 
awful lot of the time people (including myself) use essentially a ref (by 
way of a smart pointer).  Often it's due to weak ownership semantics, and 
thus iffy design, but it is what it is.

Later,
Brad