Re: [boost] call_traits

From: Simon Buchan (simon_at_[hidden])
Date: 2005-09-26 17:53:48

Graeme Prentice wrote:
> 
>>-----Original Message-----
>>From: boost-bounces_at_[hidden] 
>>[mailto:boost-bounces_at_[hidden]] On Behalf Of Simon Buchan
>>
>>Graeme Prentice wrote:
>><snipped big header>
> 
> Six lines is big?
> 
Yep.  For a header.  Consider how big the headers for a quote nested 3 
or 4 levels deep would get.

<snip>
>>You mean:
>>     template <class T>
>>     void foo( typename bar<T>::baz froble) {...}
>>is fine, but:
>>     template <class T>
>>     void foo( typename bling::bar<T>::baz froble) {...}
>>isn't? That sounds like a language flaw!
> 
> No, neither is fine.  bar<T> is a non-deduced context in both cases.  What
> makes you think the first case is fine?
> There's a good reason for this restriction even though it's a surprise when
> you first meet it.
> 
Huh.  Was I thinking of bar<T> and bar<T>::baz, then?  (I have no idea 
what I was thinking, I wrote that at something like 4AM :D)
> 
>>>>(Background info: I would like to use this technique to generate 
>>>>optimized forwarding functions that do not know anything about the 
>>>>function being forwarded to.  Overloads taking any number of params 
>>>>would be generated with the boost preprocessor library.)
>>>>
>>>>-Jason
>>>
>>>It might be better to write specializations for foo rather 
>>
>>than specify the
>>
>>>types at the point of call.
>>>
>>>Graeme
>>
>>Doesn't that defeat the point of a forwarding function? I agree that 
>>it's better than most of the alternatives, though.
> 
> How does it defeat the point of a forwarding function?
> 
> Do you mean it contradicts the requirement of the forwarding function not
> knowing anything about the function being forwarded to?  If the
> specializations (or overloads) provided are the same as the call_traits
> ones, then the forwarding function still doesn't know anything about the
> function being forwarded to.  Chances are the forwarding function will be
> inlined and the parameter types of the forwarding function won't matter so a
> single forwarding function that passes by value might do.  Using call_traits
> might even be less efficient.
*shrug*, I guess.  I probably don't quite understand what he's trying to do.