On Mon, 16 Aug 2010 08:56:51 -0400, Michel Fortin
<[email protected]> wrote:
On 2010-08-16 08:08:21 -0400, "Steven Schveighoffer"
<[email protected]> said:
On Fri, 13 Aug 2010 23:20:55 -0400, Andrei Alexandrescu
<[email protected]> wrote:
On 08/13/2010 06:35 PM, Walter Bright wrote:
Steven Schveighoffer wrote:
I like how it reads naturally. I think it's also syntactically
unambiguous. Walter, please give this one some attention, I'd love to
see this fixed.
This was endlessly discussed maybe 3 years ago. I probably invested
over
a hundred hours in trying to make it work.
It doesn't work.
Perhaps part of this is the reluctance to reexamine something which
was hard to prove correct given the ideas at the time?
However, the idea is attainable. For the simple fact that we have
tail-const references in other parts of the language. All that is
missing is syntax.
It wasn't the syntax. There were many syntaxes proposed. The type
system
loses its coherency with such a special case in it. Generic code has
weird problems, type deduction gets strange, types lose their
composability, etc.
The fact that all syntaxes proposed back then didn't cut the mustard
does not mean that no possible syntax exists. This is not NP != P.
Given that we have syntax that works for pointers, it's logical and
reasonable to assume that some syntax can work for generic
tail-constness of everything. In fact, we had syntax that *worked* it
was just confusing.
Indeed. This reflects my opinion too.
I'm not saying much about this issue right now because I feel it's no
use, or to be precise, so much time convincing is needed to bring
something useful I'd rather do something else. I've taken the route
where I'll wait until others (Andrei?) hit the same problems and put
enough pressure to force the design to be revisited. Hopefully this will
happen sooner rather than later.
Yeah, it's why I let it go before. But I think in light of the new
ability to use attributes, and the need for it in my own project
(dcollections), I want to try and push it again. I may even try my hand
at compiler hacking...
Hopefully, Andrei will eventually get around to dealing with const in
std.container and see what a mess it will become without some sort of
tail-const for ranges.
Same situation for @safe, same for pure, same for shared. Which means I
won't be adopting D2's most interesting features for some time.
BTW, I like Tomek's idea with @tail const/immutable/shared. It's not a
special case, it's a generic case, you can apply it to any type.
The idea's not bad, but I think it needs some improvments. For instance,
in a struct, I might want some members to be part of the tail and some
other not. I believe that should be allowed somehow.
What do you mean "not", meaning they are fully const? Because you can't
not apply const to references inside a const struct, that's logical const,
and while it might be a nice feature, Walter has steadfastly refused to
allow it.
If you do mean fully const, then I'm not sure why you'd want that.
-Steve
