pointer_unary_function and class member functions

[rilpo]

Hello to everybody,
I have a compile problem that relates to the use of std::pointer_unary_function with a class member function. There is a simple example :

There is MyClass.h

#include <functional>


class MyClass {
public:
	double myFunInMyClass(double v);
	void ptrFunHandle();
};

..and MyCLass.cpp

#include "MyClass.h"

double myFunOut(double v){return 0;}
double MyClass::myFunInMyClass(double v){return 0;}
void MyClass::ptrFunHandle()
{
	//std::pointer_to_unary_function<double, double> ptr_fun(this->myFunInMyClass);//does NOT compile
	std::pointer_to_unary_function<double, double> ptr_fun(myFunOut);//does compile
}

When I use the first line of ptrFunHandle function, I have the message :

erreur: no matching function for call to ‘std::pointer_to_unary_function<double, double>::pointer_to_unary_function(<unresolved overloaded function type>)’

I tried many other way to points to the function : "this->MyCLass::myFunInMyClass" rather than "this->myFunInMyClass", even "myFunInMyClass". And these attempts did not succeed. It seems natural that the type of the class member function is not known, because the class is being compiled (however, g++ could know it thanks to the .h file)..

Do you know how to solve this ?
Or do you know some other way to use a pointer on a class member function in some function pointer (i.e. not necessarily pointer_to_unary_function) ? Something clean please :-)
Thanks in advance for all answers..

[helios]

Methods are not like other functions. The main difference is that they have access to the implicit this parameter.

[Duthomhas]

Yes, the two types of function are not compatible, alas.
http://www.newty.de/fpt/index.html

[jsmith]

Use boost::bind and boost::function instead. They are much more flexible and powerful.

EDIT:

www.boost.org

#include <boost/bind.hpp>
#include <boost/function.hpp>

// Assumes this line is in a member function of MyClass to be able to use "this" pointer
boost::function< double( double )> fn( boost::bind( &MyClass::myFunInMyClass, this, _1 ) );

// Call the function
std::cout << fn( 4.0 ) << std::endl;

[rilpo]

Ok thanks you !
boost::bind and boost::function work for me !

[jsmith]

Excellent!

If you are familiar with/have used <functional>, then you might also be interested in reading up
on the boost::lambda library. In some cases*, you can avoid the extra named function altogether
by using a lambda expression. For example:

typedef std::map<char, char> CharMap;

CharMap charMap;

//...
std::for_each( charMap.begin(), charMap.end(),
    std::cout << (&boost::lambda::_1->*&CharMap::value_type::first) << " -> "
                 << (&boost::lambda::_1->*&CharMap::value_type::second) << '\n' );

Outputs the entire contents of the map, without having to write operator<< for std::pair<char, char>.

*lambda expressions can get quite complicated, and despite lambda support for doing almost anything (if-else, switch, while, try, catch, etc), often times for readability's sake it is better to create a named function anyway.