From: Daryle Walker (darylew_at_[hidden])
Date: 2004-01-28 16:25:19
On 1/27/04 7:39 PM, "Howard Hinnant" <hinnant_at_[hidden]> wrote:
> On Jan 27, 2004, at 11:06 AM, Peter Dimov wrote:
>
>>> Need to be? No. But I still like it. <shrug> I was convinced because
>>> that's how a newbie expected it to work.
>>
>> I'm starting to not like it. :-) The problem is:
>>
>> template<class X> void f(S_ptr<X> px);
>>
>> where f doesn't support arrays. A reasonably common occurence. S_array<>
>> doesn't match, but S_ptr<T[]> does. The author of f would need to learn about
>> enable_if to prevent array pointers from being passed to f. This is not good,
>> although the exact degree of not-goodness is somewhat debatable.
>
> I understand your hesitation. But I'm not yet seeing a concrete case to
> support it.
>
> There are two situations to analyze here:
>
> 1. Client writes:
>
> template<class X> void f(S_ptr<X> px);
>
> and intends to catch only pointers to single objects, and does not want
> to deal with pointers to arrays.
>
> 2. Client writes:
>
> template<class X> void f(S_ptr<X> px);
>
> and intends to catch pointers to both single objects and array objects.
>
> In case 1, learning about enable_if is not necessarily a bad thing.
> Indeed, a significant portion of the standard headers would be much
> better behaved today if we (as a community) had better understood the
> value of restricted templates, how to implement them, and the dangers
> of templates with unrestricted syntax, but restricted semantics. For
> example:
[TRUNCATE]
If the solution to the "S_ptr<X[]>" idiom is to study up some more on other
C++ idioms, then I think that we have a Big Red Flag that something is wrong
with the new idiom. There are two things I read about in GUI programming:
1. Don't make a big deal of differentiating things that are similar.
2. Don't hide differences that matter.
The C++ committee screwed up [2] with std::vector<bool>. I don't want
another screw-up introduced, especially if it's more insidious and
deliberate. (i.e. We should let this idiom die.)
-- Daryle Walker Mac, Internet, and Video Game Junkie darylew AT hotmail DOT com