Is it possible to change the member function pointer from std::bind to lambda?

Question

I coded callback method with std::function, std::bind.

std::function object func1 in class A point to function bFoo(int, int) which is member of class B.

My callback code in my program:

// Class A - A.h
class A
{
  public:
    template<class T>
    void setCallback(T *pClass, void(T::*pFunc)(int, int));

  private:
    std::function<void(int, int)> func1;
}

template<class T>
inline void A::setCallback(T *pClass, void(T::*pFunc)(int, int))
{
  func1 = std::bind(pFunc, pClass, std::placeholders::_1, std::placeholders::_2); 
}

// Class A - A.cpp
...
func1(x,y);
...

// Class B - B.h
class B
{
  public:
    void bFoo(int x, int y);

  private:
    A a; // instance of class A
}

// Class B - B.cpp
B::B()
{
  a.setCallback(this, &B::bFoo);
}

It works fine.

However, I heard that in C++ 14 and higher, std::bind can be completely replaced by lambda, and lambda has many advantages over std::bind.

So I tried to change the bind to lambda and looked up many examples, but in my case I haven't found how to replace bind to lambda.

I want to assign a member function from another class into std::function using lambda, not std::bind.

is this possible?

Answer 1

It would be possible to do it with your current code by using

func1 = [=](int x, int y){ (pClass->*pFunc)(x,y); };

In my opinion it's probably better to write out the lambda at the calling site instead. To do that you need to modify setCallback.

class A
{
  public:
    template<class T>
    void setCallback(T callback);

  private:
    std::function<void(int, int)> func1;
}

template<class T>
inline void A::setCallback(T callback)
{
  func1 = callback; 
}

Then we can call from Bs constructor with a lambda.

class B
{
  public:
    void bFoo(int x, int y);

  private:
    A a; // instance of class A
}

// Class B - B.cpp
B::B()
{
  a.setCallback([&](int x, int y){ bFoo(x, y); }); // & will capture this
}