How to use signaler/listener in aGrUM ?

aGrUM has its own implementation of signalers/listeners.

Let's say that class A has a method f(int i,char ch) and would like to give to everyone the right to know whenever f() is run.

#include <agrum/core/signal/signaler.h>
 
class A {
 public:
  gum::Signaler2<int,char> onF; // Note that onF is public and will send an int and a char then
'Signaler2' is used.
 
 void f(int i,char ch) {
    //do something
    GUM_EMIT2(onF,i,ch); // a signal (with 2 args i and ch) is emitted via the Signaler onF.
  }
};
 @

Note that for class A, adding signaler is very light : a new public attribute and a GUM_EMITx when needed (where x is the number of args).

Now, how to listen to such a signal ?

#include <agrum/core/signal/Listener.h>
 
class B : public gum::Listener {
 public:
  void whenF(const void *src,int i, char ch) { // note the void* src
    std::cout<<"object "<<src<<" run f on "<<i<<" and "<<ch<<std::endl;
  }
};
// we may have more than one listener
class C : public gum::Listener {
 public:
  void dummy(void *src,int i,char ch) {
    std::cout<<"dummy on "<<i<<" and "<<ch<<std::endl;
  }
};

Now we have to connect

int main(void) {
  A a;
 
  B b1;
  B b2;
 
  GUM_CONNECT( a,onF,b1,B::whenF );
  GUM_CONNECT( a,onF,b2,B::whenF );
 
  a.f(3,'a');
  // b1.whenF and b2.whenF has been executed.
 
 
  {
    C c;
    GUM_CONNECT( a,onF,c,C::dummy );
    a.f(4,'x');
    //c.dummy(), b1.whenF and b2.whenF has been executed.
  } // c is destroyed...
 
  a.f(5,'y');
  //b1.whenF and b2.whenF has been executed.
}