Re: [Boost-users] Iterate over template arguments

24 Nov 2011


      On 11/23/2011 04:33 PM, Allan Nielsen wrote:
...
...
It might be me which does not understand it, but as I read the
documentation funciton_types is for manipulating functions pointers,
not to manage template arguments...
Please correct me if I'm wrong
Okay, I got it...  is one template argument...
:
typename boost::function_types::result_type<T0>::type is the return
type, and I can use parameter_types and MPL to iterate over the
parameters. Clever..
But how do I implement the call interface:
template<typename T>
struct IfCall {
     typedef typename boost::function_types::result_type<T0>::type R;
R call( /* T0, T1, T2...*/ ) { // can I get the MPL sequence into
the method signature??
     }
};
You need to use the preprocessor for this; in that case, you can also 
get rid of Boost.FunctionTypes.

#include 
#include 
#include 
#include 

#define IFCALL_MAX_ARITY 5

template<class Sig>
struct IfCall;

#define M0(z, n, t)                                                    \
template\
struct IfCall                           \
{                                                                      \
     R call(BOOST_PP_ENUM_BINARY_PARAMS(n, A, const& a))                \
     {                                                                  \
         return R();                                                    \
     }                                                                  \
};                                                                     \
/**/

BOOST_PP_REPEAT(BOOST_PP_INC(IFCALL_MAX_ARITY), M0, ~)
#undef M0

Re: [Boost-users] Iterate over template arguments

Mathias Gaunard