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>  -----Original Message-----
>  From: boost-bounces@[...].org 
>  [mailto:boost-bounces@[...].org] On Behalf Of Jason Hise
>  Sent: Sunday, 25 September 2005 2:11 p.m.
>  To: boost@[...].org
>  Subject: [boost] call_traits
>  
>  
>  Why doesn't the following compile?  I get the error "foo: 
>  function does 
>  not take 1 arguments" on VC8.
>  
>  #include <boost/call_traits.hpp>
>  
>  template < typename P1 >
>  void foo ( typename ::boost::call_traits < P1 >::param_type p1 )
>  {
>  }
>  
>  int main (  )
>  {
>      foo ( 42 ); // error here
>      return 0;
>  }



This is the infamous non-deduced context.  A nested name specifier
(call_traits) is a non-deduced context so P1 cannot be deduced.  You have to
write foo<int> (42).  This is like an invisible cast, so you have to remember
to change all the explicit type specifiers if you change the type of an
argument being passed in such a function.


>  
>  (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


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