D's greatest mistakes

[Andrei Alexandrescu]

On 11/29/10 1:49 PM, Steven Schveighoffer wrote:
> On Mon, 29 Nov 2010 14:38:40 -0500, Andrei Alexandrescu
> <SeeWebsiteForEmail at erdani.org> wrote:
>
>> On 11/29/10 1:35 PM, Steven Schveighoffer wrote:
>>> On Mon, 29 Nov 2010 11:52:31 -0500, dsimcha <dsimcha at yahoo.com> wrote:
>>>
>>>> == Quote from Andrei Alexandrescu (SeeWebsiteForEmail at erdani.org)'s
>>>> article
>>>>
>>>>> Ultimately I believe we need to make Rebindable palatable. That would
>>>>> have the nice side effect of enabling other proxy types.
>>>>> Andrei
>>>>
>>>> I've asked before and I'll ask again, what's still wrong with
>>>> Rebindable? A bunch
>>>> of alias this issues got fixed in 2.050, and I fixed a bunch of misc.
>>>> convenience
>>>> issues a few releases ago. I fail to see the problem with it anymore.
>>>
>>> Every few months or so, someone finds a problem with it. It seems that
>>> it's good enough in theory, but miserably fails in practice when someone
>>> tries to use it. I admit I haven't looked at it in a while, but there
>>> are implicit casting problems that cannot be solved without compiler
>>> help. I just think Rebindable will get more and more convoluted until
>>> someone finally admits that this is better served as a builtin feature.
>>
>> I don't grok this. If people find different issues with it that are
>> fixed, then there is progress, right? (Clearly "escaping" into the
>> language makes things better.)
>
> At some point, Rebindable may be as good as a language feature. But we
> haven't got there yet. And we haven't got there in years. And I don't
> see us getting there in the forseeable future -- there are too many
> implicit casting problems to solve.
>
> At the point where it does become useable, how big will it be? How much
> will it slow down compilation? How specialized do we have to make code?
>
> Const is supposed to be a compile-time feature, optimized out at
> runtime. If Rebindable isn't completely removed from the code
> generation, then it is not a complete feature.

I don't think compilation speed and runtime speed are the main 
challenges. All of Rebindable's methods are one-liners. The issue with 
Rebindable is integration within the type system.

>>> One of those issues:
>>>
>>> import std.typecons;
>>>
>>> class C {}
>>>
>>> void foo(Rebindable!(const C) c)
>>> {
>>> }
>>
>> Let me fix that:
>>
>> void foo(const C c)
>> {
>> auto rc = Rebindable!(const C)(c);
>> ...
>> }
>
> You missed the point.. completely :)
>
> please look at bar.

You're right. bar is the part that alias this needs to take care of. So 
in a way this is an easier problem to solve.


Andrei