-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Jason Hise Sent: Sunday, 25 September 2005 2:11 p.m. To: boost@lists.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