Re: [boost] boost::result_of and C++03

From: Eric Niebler (eric_at_[hidden])
Date: 2008-04-07 12:38:07

Peter Dimov wrote:
> Eric Niebler:
> 
>> // lvalue
>> result_of<identity(int &)>::type l = identity()(i);
>> assert( &l == &i );
> 
> Does this really compile for you?

Yes.

#include <cassert>
#include <boost/utility/result_of.hpp>

struct identity
{
     template<typename Sig>
     struct result;

     template<typename This, typename Arg>
     struct result<This(Arg)>
     {
         typedef Arg type;
     };

     template<typename Arg>
     Arg &operator()(Arg &arg) const
     {
         return arg;
     }

     template<typename Arg>
     Arg const &operator()(Arg const &arg) const
     {
         return arg;
     }
};

int main()
{
     using boost::result_of;

     int i = 0;
     int const j = 0;

     // rvalue
     result_of<identity(int)>::type k = identity()(1);
     assert( 1 == k );

     // lvalue
     result_of<identity(int &)>::type l = identity()(i);
     assert( &l == &i );

     // const lvalue
     result_of<identity(int const &)>::type m = identity()(j);
     assert( &m == &j );
}

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com