Re: [boost] Re: compile-time binary constants

From: David Abrahams (dave_at_[hidden])
Date: 2003-01-19 12:59:16

Gennaro Prota <gennaro_prota_at_[hidden]> writes:

> On Sun, 19 Jan 2003 09:42:51 -0500, David Abrahams
> <dave_at_[hidden]> wrote:
>
>>>>For another thing, it would be a compile-error if the
>>>>expression *can* be implicitly converted to the destination type,
>>>>which makes no sense to me.
>>>
>>> Isn't this the intent? 
>>
>>I don't know what the intent is; you never explained that to me.  What
>>this does is to static_cast only when it must be forced (often in the
>>"unsafe" direction); it was hard to see how that could be useful.
>>Maybe just as a way of stating and checking that you know what you're
>>doing?
>
> Well, actually I did it just for the fun of it. The original thread
> was about implicit_cast, not explicit, and I added some thoughts. In
> any case the comment I've made here about the comma operator applies
> to the implicit piece as well:
>
>   template <typename T>
>   char implicit_cast (typename identity<T>::type x) {
>       return x;
>   }
>
>   // incomplete return type now is here
>   template <typename T>
>   void implicit_cast (...);
>
>   #define IMPLICIT_CAST(dst_type, expr)                 \
>             ( sizeof( implicit_cast<dst_type>(expr) )   \
>                        ,                                \
>               static_cast<dst_type>(expr)               \
>             )

Why wouldn't you just write implicit_cast<dst_type>(expr) in this
case?  Are you trying to save copies?

(You might think I'm not interested in the comma operator issue.  I
guess you'd be right.  It would be good to do something about it, but
I don't feel strongly.  If you do, you will have to champion it).

-- 
                       David Abrahams
   dave_at_[hidden] * http://www.boost-consulting.com
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