Hicham, it does not create a new new type it only declares a type. Consider the following example: template struct X {}; This means your type X expects a function pointer type with return value int and no parameters. This can be used in a meta programming to make some type assumptions or inspection. This is how the result_of works. Think of result_of as of type X but a bit more complex and which can give an assumption about the function type passed. We can write: template struct X { typedef int type; }; A more generic form would be if int would be any valid result type T, so that we could write smth like this: template struct X { typedef T type; }; Actually this is not a legal C++ struct, since T was not declared as template parameter, but think of it as if it would. template struct X { typedef T result_type; typedef MyFunc function_type; }; Here MyFunc is a name of the function pointer type, which allows us to reference this type from inside the template. Hope that helps. With Kinds regards, Ovanes On Thu, May 1, 2008 at 2:32 PM, Hicham Mouline wrote:

But "floatfct" was defined earlier as the type of a pointer to a function with only 1 arg float. just passing the template argument to result_of creates a new type? is the new type also called floatfct ?

----- Original Message ----- From: "Ovanes Markarian" To: boost-users@lists.boost.org Subject: Re: [Boost-users] boost::result_of error? Date: Thu, 1 May 2008 13:58:21 +0200

Hicham,

as far as I understand your code you pass to result_of a new type: typedef typename boost::result_of::type resultype;

This type is a pointer to a function type, which has as return type a pointer to floatfct and as params float, float. That's why it compiles.

Regards, Ovanes

On Thu, May 1, 2008 at 1:25 PM, Hicham Mouline wrote:

...

Hello, trying out Pete Becker's "c++ std lib ext" exercises, ex1 p155

#include <iostream> #include <typeinfo> #include

typedef float (*floatfct)(float); int main(int argc, char* argv[]) { typedef typename boost::result_of::type resultype; std::cout<< typeid(resultype).name() << std::endl; }

should fail, because result_of is instantiated with a callable type with 2 float args, while it's been defined as taking 1 float arg only?

with intel10.1-MSVC8-boost1.35, it links.

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