Re: [boost] move_ptr

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