Using std::bind on template class member - c++

Question

Consider the code below
#include <iostream>
#include <functional>
class Solver{
public:
int i = 0;
void print(){
std::cout << "i solved" << std::endl;
}
};
template <typename T> class ThingHandler{
public:
template <typename B,typename C>
void handleThing(T& solver,B paramOne,C paramTwo){
std::cout << "i handled something " << std::endl;
solver.print();
std::cout << paramOne << paramTwo;
}
};
class CantHandle{
public:
void needHelp(std::function<void(int,int)> handleThing){
int neededInt = 0;
int neededIntTwo = 2;
handleThing(neededInt,neededInt);
}
};
int main() {
ThingHandler<Solver> thingHandler;
CantHandle cantHandle;
Solver solver;
solver.i = 10;
auto fp = std::bind(&ThingHandler<Solver>::handleThing<Solver,int,int>,
thingHandler,solver,std::placeholders::_1,std::placeholders::_1);
//the row above is what I want to achieve
cantHandle.needHelp(fp);
return 0;
}
I'm getting the following error:
140: error: no matching function for call to ‘bind(, ThingHandler&, Solver&, const
std::_Placeholder<1>&, const std::_Placeholder<1>&)’ 37 | auto
fp = std::bind(&ThingHandler::handleThing,
thingHandler,solver,std::placeholders::_1,std::placeholders::_1);
What I want to do is have a generic class that solves some problem. Then call upon a specialization of that class. So in the case above I want ThingHandler to be (Solver& solver, int paramOne, int paramTwo). I'm not quite sure how to achieve this.

Answer 1

Member function you bind takes two template type parameters, so Solver is redundant in template argument list.
Should be:
&ThingHandler<Solver>::handleThing<int,int>
Some remarks: your code binds handleThing for a copy of thingHandler instance.
Also first bound parameter - solver, is copied into functor generated by bind.
If you want to avoid these two copies, use & or std::ref:
auto fp = std::bind(&ThingHandler<Solver>::handleThing<int,int>,
&thingHandler,std::ref(solver),std::placeholders::_1,std::placeholders::_2);