On Mon, 13 Oct 2008 23:32:30 -0400, Tommy M. McGuire <[EMAIL PROTECTED]> wrote:
> Andrew Coppin wrote:
>> Bulat Ziganshin wrote:
>>> people that make critique on haskell type classes, don't take into
>>> account that it's unlike C++ templates, implemented via run-time
>>> dictionaries and other modules may define new instances
>>
>> Personally, I have no clue how C++ templates work [yet]. (As in, I'm
>> learning C++, but I haven't got to that chapter yet.)
>>
>> Some guy told me that templates are "the best feature in the language",
>> and proceeded to show me a huge chunk of highly complex-looking code
>> which is approximately equivilent to
>>
>> join :: Array x -> Array x -> Array x
>>
>> I was unimpressed.
>>
>> Actually, that's a lie. I was impressed that such a low-level language
>> could manage even that much abstraction. But I still prefer the Haskell
>> way...
>
> C++ values have sizes:
>
> class foo {
> int x;
> };
>
> is half (ahem; make that "different from") the size of
>
> class bar {
> int x;
> int y;
> };
>
> As a result, doing parametric polymorphism requires duct taping
> something suspiciously similar to cpp macros to the type system. Hence,
> how C++ templates work: weirdly.
>
> Java (and presumably C#) "generics" are very much like a weakened
> version of normal parametric polymorphism. C++ templates are an attempt
> at the same thing in a completely different landscape. I'd be willing
> to bet that Some Guy's code was very close to exactly equivalent to your
> join.
>
> Now, as to what C++ templates have to do with Haskell type classes, I
> dunno...
In the next C++ standard, type checking capabilities are being added to
templates---"concepts" specify a set of operations a templated type must
support. See <http://en.wikipedia.org/wiki/C%2B%2B0x#Concepts>. Seems
somewhat similar to Haskell typeclasses to me, but perhaps the similarity is
merely superficial. :-)
Regards,
Brad Larsen
_______________________________________________
Haskell-Cafe mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/haskell-cafe
