Reference counted containers prototype

[Andrei Alexandrescu]

On 12/27/11 9:27 AM, Michel Fortin wrote:
> On 2011-12-27 14:57:18 +0000, Andrei Alexandrescu
> <SeeWebsiteForEmail at erdani.org> said:
>> I talked a lot about this with Walter and we concluded that the story
>> with const and immutable goes like this: in a RefCounted!T object, the
>> T is constant, not the RefCounted. So it would be
>> RefCounted!(immutable T).
>
> That'll work, but I'm not sure where you're getting at with this.
>
> Instead of writing "const DList!T" as the parameter type in your
> function you have to write "RefCounted!(const DListImpl!T)"? Isn't that
> worse than "ref const DList!T"?

That's an issue we're thinking about how to address.

>> Not to seem dismissive, but this sounds quite complicated for what it
>> does. Could we implement it as a library feature? And assuming your
>> motivating argument wasn't as strong, is it needed?
>
> It can't be a library feature because it requires the compiler to
> implicitly add a "ref" to functions parameters when they are of a "ref
> struct" type. That's pretty much all it does: add a flag to struct
> types, implicitly add "ref" to parameters based on that flag.

Anyhow, I think a feature would need to be tremendously justified and 
with a huge power/weight ratio. This one I actually find ill-designed 
because now I can't look at the body of a function to figure 
pass-by-value vs. pass-by-reference - I also need to look at the 
definition (what if it was a ref struct?). One more non-modular thing to 
keep in mind. This is not going to fly.

> I'm not sure why you think it's complicated. Perhaps I should just not
> have talked about rvalues: that's a separate benefit you can built on
> top of it by adding one or two lines of code in DMD, but it's a separate
> thing.

I think the "But there's one more thing" did it to me.


Andrei