Nabble - Gnome - Libsigc

/** If you have pkg-config, then you can compile this file for example like this:

 * c++ -Wall `pkg-config --cflags --libs sigc++-2.0` sigcpp.cpp

 */

#include <iostream>

#include <sigc++/sigc++.h>

class Parent {

public:

        int f (int i, double d, char c);

};

int Parent::f (int i, double d, char c) {

        std::cout << "Parent::f" << std::endl;

        return 0;

}

class Child : public Parent {

public:

        int g (int i, double d, char c);

};

int Child::g (int i, double d, char c) {

        std::cout << "Child::g" << std::endl;

        return 0;

}

typedef sigc::slot<int, Parent *, int, double, char> sp;

typedef sigc::slot<int, Child *, int, double, char> sch;

typedef sigc::mem_functor3<int, Parent, int, double, char> mfp;

typedef sigc::mem_functor3<int, Child, int, double, char> mfch;

typedef sigc::mem_functor4<int, Parent, int, double, char, char *> mfp4;

typedef sigc::mem_functor4<int, Child, int, double, char, char *> mfch4;

int foo (void) {

        Parent p;

        Child ch;

        mfp a_p = sigc::mem_fun(& Parent::f); 	// <-- This works.

        a_p(& p, 0, 1.0, 'c');	/// <-- Works

        a_p(& ch, 0, 1.0, 'c');	/// <-- Works

//	mfp a_ch = sigc::mem_fun(& Child::g); 	// <-- Doesn't work, which seems strange.

//	Compile error: conversion from âsigc::mem_functor3<int, Child, int, double, char>â to non-scalar type âmfpâ requested

//	mfch b_p = sigc::mem_fun(& Parent::f);	// <-- Doesn't work, but this seems correct, because of conversion from Parent to Child.

//	Compile error: conversion from âsigc::mem_functor3<int, Parent, int, double, char>â to non-scalar type âmfchâ requested

        mfch b_ch = sigc::mem_fun(& Child::g);	// <-- This works.

//	b_ch(& p, 0, 1.0, 'c');		/// <-- Doesn't work, but this is OK.

//	Correctly displayed error message: invalid conversion from âParent*â to âChild*â

        b_ch(& ch, 0, 1.0, 'c');	/// <-- Works

        sp c_p = sigc::mem_fun(& Parent::f);	///  <-- This works

        c_p(& p, 0, 1.0, 'c');		/// <-- Works

        c_p(& ch, 0, 1.0, 'c');		/// <-- Works

//	sp c_ch = sigc::mem_fun(& Child::g);	///  <-- This does not work, which seems also strange.

//	Compile error: invalid conversion from âParent* constâ to âChild*â

        sch d_p = sigc::mem_fun(& Parent::f);		///  <-- This compiles, which is strange.

//	d_p(& p, 0, 1.0, 'c');		// <-- But this refuses to compile, which is correct.

//      Correctly displayed error message: invalid conversion from âParent*â to âChild*â

        d_p(& ch, 0, 1.0, 'c'); 	// <-- Works

        sch d_ch = sigc::mem_fun(& Child::g);		///  <-- This works

//	d_ch(& p, 0, 1.0, 'c');		/// <-- Doesn't work, but this is OK.

//	Correctly displayed error message: invalid conversion from âParent*â to âChild*â

        d_ch(& ch, 0, 1.0, 'c');	/// <-- Works

        // I would like to ask for explnation of how to work-around this previously mentioned error:

        //

        // Error: invalid conversion from âParent* constâ to âChild*â

        //

        // First, why the `const` is added there?

        /** I agree that this error is in some way reasonable and I know that this usage of functors is not exactly correct.

         *  But is there a correct usage, then?

         *  

         *  What I would like to achieve:

         *  

         *  Have a generic functor, to which I would be able to assign a member function

         *  of arbitrary class derived from the previously specified base class. The only limitations

         *  would be the number of parameters and the type of parameters. I would also like to be able

         *  to alter the number of parameters as well as their type by standard means of sigc++ library.

         *  

         *  The most important is that I would like this functor to behave as the unbound member functor,

         *  so I would be able to choose the instance from which the member function will be called.

         *

         *  How can I achieve something like this?

         */

        return 0;

}

int main (int argc, char ** argv) {

        std::cout << foo() << std::endl;

        return 0;

}

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