Re: [Boost-users] boost::result_of error?

From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2008-05-01 13:45:45

Please read below. Just got an angry email from some pedantic Mailing-List
guard.

On Thu, May 1, 2008 at 6:07 PM, Hicham Mouline <hicham_at_[hidden]> wrote:

> Thanks for your clarifications,
>
> In your example, if "MyFunc" was typedef'd before its use in the template
> argument as say
>     typedef  int (*MyFunc)(int);
> it would not conflict with its use in the template argument ?
>
First of all. I am sorry for an error I made when stated:

template<T MyFunc()>
struct X
{
   typedef T             result_type;
   typedef MyFunc   function_type;
};

This is not a valid C++ code, since MyFunc as the template parameter is a
real pointer to a function, it is not a type. And you cannot make a typedef
for a pointer. Only for it's type.

To visualize the usage I have written a small program:

#include <iostream>
#include <typeinfo>

typedef int (*MyFunc)(int, int);

int get_int(int x)
{
    return x;
}

int plus(int x, int y)
{
    return x+y;
}

template<int (*MyFunc)(int)>
struct X
{
  typedef int           result_type;

  result_type exec()const
  {
      ::MyFunc f2 = &plus; //use scope resolution to access the global
MyFunc
      return MyFunc(10)+f2(10,10);
  }
};

int main(int argc, char* argv[])
{
    X<&get_int>    x;
    std::cout << "sum: " << x.exec() << "\n";
}

> best regards,
>
>