Signals2 connect() usage with templates - c++

Question

I am trying to create template classes for some repetitive functions that will be required for sending data around, of different types. However, my issue (I think) is really with InterfacePublisher::addSubscription() function that is utilizing boost::signals2::signal::connect().
It seems like connect function is taking the location of the base classes, even though derived classes override them. I am sure there is going to be a fix for this but am stuck with it for a long while now.
I am pasting my code below. The idea is to pass a string from StringPublisher to StringSubscriber without hard-coding the class names through the templates:
#include <string>
#include <iostream>
#include <boost/lambda/lambda.hpp>
#include <boost/signals2/signal.hpp>
#include <boost/signals2/signal_base.hpp>
#include <boost/signals2/slot.hpp>
#include <boost/signals2/slot_base.hpp>
template <class T>
class InterfaceSubscriber
{
public:
InterfaceSubscriber(const std::string& name)
: mName (name) {}
virtual void onData (const std::string& source, T& data)
{
std::cout << "InterfaceSubscriber::onData::BASE SHOULD BE IGNORED\n";
}
protected:
const std::string mName;
};
template <class T>
class InterfacePublisher
{
public:
InterfacePublisher(const std::string& publisherName)
: mPublisherName (publisherName)
{
}
void publish(T& data)
{
mSignalArgs(mPublisherName, data);
}
void addSubscription (InterfaceSubscriber<T>* subsc)
{
// The section where I think problem is. There is where the solution should be
mSignalArgs.connect( std::bind (InterfaceSubscriber<T>::onData , *subsc, std::placeholders::_1, std::placeholders::_2) );
}
protected:
boost::signals2::signal<void (const std::string& publisherName, T& data)> mSignalArgs;
const std::string mPublisherName;
};
class StringSubscriber : public InterfaceSubscriber<std::string>
{
public:
StringSubscriber (const std::string& subscName) : InterfaceSubscriber(subscName) {}
void onData (const std::string& source, std::string& data) override
{
std::cout << mName << ":[" << source << "]Received string of value: " << data << std::endl;
}
};
class StringPublisher : public InterfacePublisher<std::string>
{
public:
StringPublisher (const std::string& name) : InterfacePublisher(name) {}
};
int main()
{
StringSubscriber subscriber1("String_Subscriber_1");
StringSubscriber subscriber2("String_Subscriber_2");
StringPublisher publisher("Publisher_Of_String");
publisher.addSubscription(&subscriber1);
publisher.addSubscription(&subscriber2);
std::string str = "Hello World";
// This should lead to StringSubscriber::onData being called, but instead ends up calling InterfaceSubscriber<T>::onData
publisher.publish(str);
}

Answer 1

StringSubscriber is being sliced during the construction of the std::bind functor, resulting in InterfaceSubscriber<T>::onData() executing on an object with a runtime type of InterfaceSubscriber<T> rather than the runtime type of the object provided to InterfacePublisher<T>::addSubscription().
void addSubscription(InterfaceSubscriber<T>* subsc)
{
mSignalArgs.connect(std::bind(&InterfaceSubscriber<T>::onData,
*subsc, ...);
// ^~~ sliced
}
To resolve this, either pass the pointer directly or pass a std::ref object as the instance.
void addSubscription(InterfaceSubscriber<T>* subsc)
{
mSignalArgs.connect(std::bind(&InterfaceSubscriber<T>::onData,
subsc, ...);
// ^~~ pointer
}
or
void addSubscription(InterfaceSubscriber<T>* subsc)
{
mSignalArgs.connect(std::bind(&InterfaceSubscriber<T>::onData,
std::ref(*subsc), ...);
// ^~~ reference
}