[boost] Re: call_traits

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2004-07-05 19:52:55

On Jul 5, 2004, at 7:46 PM, David Abrahams wrote:

> "Edward Diener" <eddielee_at_[hidden]> writes:
>
>> What are the issues with call_traits which make it unusable ?
>
> As far as I can tell, there is no clear documentation of what
> _precisely_ any partcular member of call_traits<T> is for a given T.
> It's even less clear what fallback the library uses when a full
> implementation of call_traits would require partial specialization
> that isn't available.
>
> It seems as though the documentation is intended to be a more abstract
> description of what happens, but it leaves me (at least) feeling very
> unclear about what I'm actually getting.
>
> It's also unclear to me what purpose is served by the "reference" and
> "const_reference" members.

As I recall, call_traits was intended to work around the "reference to 
reference" problem for both parameters and return types.  This problem 
has since been solved by cwg #106 ( 
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#106 ).  
Though I'm unsure how widely implemented this dr is in current 
compilers.  I initially viewed call_traits as a way to optimize whether 
a type should be passed by const ref or by value.  But I was mistaken.  
The real value was in passing/returning reference types without bumping 
into the reference-to-reference problem.

-Howard