函子重载最佳做法

Question

Hi I am trying to get to grips with functors. Here is a simple example

struct A {
 double b,c;
 A(const double bb, const double cc) : b(bb), c(cc) {}
 double operator()(const double x, const double y) {
  return b*c*x*y;
 }
};

I would like to know if it is possible to overload A such that it could be passed b , c and also eg x reusing the code in the operator() . My overall interest is to not have to re-write lengthy code in operators multiple times and to better understand the best practices for doing this.

Thanks!

Answer 1

One method of doing this is with std::bind in <functional> . This returns a closure that you can call without arguments. An alternative would be to create a new constructor with default arguments for a and b , or a derived class, and overload it to have:

double operator()(const double x = m_x, const double y = m_y);

As a side note, please don't use the same names for members and arguments of member functions; that creates ambiguity about which you mean and could even cause bugs if you rename a parameter later.

Answer 2

I would like to know if it is possible to overload A such that it could be passed b, c and also eg x reusing the code in the operator().

Yes, it is not difficult to do that.

double operator()(double x, double y) // Remove the const. It's useless.
{
   // Call the other overload using the member data.
   return (*this)(b, c, x, y);
}

double operator()(double bb, double cc, double x, double y)
{
   // Not using any member data at all.
   return bb*cc*x*y;
}