Most general way to receive a functor as a parameter? - c++

Question

I am writing a wrapper for a multithreaded scheme. It should operate similar to a timer.
I have a particular class (clock) that implements a function called tick which should be passed to constructor. How do I describe a C++ style function (myClass::myfunction, as opposed to the C convention) as the parameter to a method or constructor?
Would anybody be kind enough to show me the declaration for this kind of constructor?
clock myInstance(otherClass::aMethod)
myInstance.tick(); // Should call otherClass::aMethod
myInstance.tick();
Does C++11 and Bind help?

Answer 1

You can either call a static member function of a class or a non-static member function of an object. A non-static member function needs to have the context of an object (this pointer).
Here's a simplified example of how you can use functors and bind to call a member function.
#include <functional>
class clock
{
public:
clock(const std::function<void()>& tocall) : m_tocall(tocall) {}
void tick() {m_tocall();}
private:
std::function<void()> m_tocall;
};
class otherclass
{
public:
void aMethod() {}
};
int main(int argc, char *argv[])
{
otherclass A;
clock c( std::bind(&otherclass::aMethod, &A) );
c.tick(); // Will end up calling aMethod() of object A
}

Answer 2

You need not to use std::function for this. You need to have TWO pointers: One is the class-object, and one to the method of that class. In simple terms, you need to make it able to do:
CallNonVirtual(pClassPtr, pFuncAddr);
And therefore, you need both parameters, so that you can actually call it like:
(pClassPtr->*pFuncAddr)(); // Assuming no parameter
For this, you can do:
class Clock
{
COtherClass* pClassPtr;
/// Typedef simplifies
typedef void (COtherClass::*TargetFuncType)();
TargetFuncType pFuncAddr;
public:
Clock(COtherClass* pOther, TargetFuncType pFunc) :
pClassPtr(pOther), pFuncAddr(pFunc)
{
}
void tick()
{
(pClassPtr->*pFuncAddr)();
}
};
And make a call:
int main()
{
COtherClass Obj;
Clock theClock(&Obj, &COtherClass::TheNonStatic);
theClock.tick();
}