[boost] Re: Implicitly-Callable Functions in C++0x?

From: Daniel Frey (daniel.frey_at_[hidden])
Date: 2004-03-12 08:09:02

David Abrahams wrote:
> Daniel Frey <d.frey_at_[hidden]> writes:
> 
> 
>>Thorsten Ottosen wrote:
>>
>>>"Paul A Bristow" <boost_at_[hidden]> wrote in message
>>>news:001501c40795$ce631ce0$0c010101_at_hetp3...
>>>
>>>
>>>>>From a very quick study of this, this radical proposal avoids nasty
>>>>brackets "pi()" by adding a new C++ keyword implicit to make "pi" have
>>>>the same effect.
>>>
>>>Considering what Daniel can do, I don't think the math constant part
>>>of the
>>>proposal brings anything.
>>
>>Basically, I agree. When I sorted out the VC-issues and finished the
>>documentation, I'll have a deeper look at the ICF-proposal and post
>>some comments to csc++. FWIW, my gut feeling is that the proposal it
>>not worth the trouble.
>>
>>However: I can do many, but not all things proposed. There is one
>>thing (syntax) that I cannot do but that I like very much:
>>
>>pi<T>
>>
>>In my constant library, this is spelled 'pi.get<T>()'. Alternatives
>>that don't work: 'static_cast<T>(pi)', 'T(pi)', 'pi.operator T()'. If
>>anyone has a cool idea how this can be improved, let me know :)
> 
> 
>    get<T>(pi)

Good idea, I'll think about this one.

> Why doesn't 
> 
>    T(pi)

Because T can have multiple ctors (taking i.e. float, double, long 
double and thus making the conversion ambiguous - I can't control that 
from inside pi, the T is not exactly forwarded to pi's type when asked 
for a conversion).

The second reason is that it limits the result to T. When I have a unit 
library, this is not acceptable, as get<T> provides some magic: 
get<double>(G) returns a combination of a double value plus the 
appropriate unit, not a plain double.

This is the basic problem of all the alternatives I mentioned: I don't 
have the freedom to modify the returned type, but this is an essential 
feature I need.

Regards, Daniel

-- 
Daniel Frey
aixigo AG - financial solutions & technology
Schloß-Rahe-Straße 15, 52072 Aachen, Germany
fon: [phone], fax: [phone]
eMail: daniel.frey_at_[hidden], web: http://www.aixigo.de