function wrap

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This post will introduce a C++ 11 feature, std::function. It can wrap any kind of callable element into a copyable object and whose type depands soly on its call signature.

std::function is an object who can replace the function poiner in C language but more safety. It is useful for implement of many C++ design patterns.

std::function
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#include <cstdlib>
#include <functional>
#include <vector>
typedef std::function<int(int,int)> IntOpFun;
struct Adder {
  int OnAB(int iA, int iB) {
    printf("Add(%d,%d)=%d", iA, iB, iA + iB);
    return iA + iB;
  }
};
 
struct Muler {
  int OnAB(int iA, int iB) {
    printf("Mul3(%d,%d)=%d", iA, iB, iA * iB);
    return iA * iB;
  }
};
struct Subject {
  void AddObserver(IntOpFun of) {
    m_vecOf.push_back(of);
  }
 
  void Notify(int iA, int iB) {
    for (auto iter = m_vecOf.begin(); iter != m_vecOf.end(); ++iter) {
      (*iter)(iA, iB);
    }
  }
  std::vector<IntOpFun> m_vecOf;
};
int main() {
  Subject3 subj;
  Adder3 adder;
  Muler3 muler;
  subj.AddObserver(std::bind(&Adder3::OnAB, &adder, std::placeholders::_1, std::placeholders::_2));
  subj.AddObserver(std::bind(&Muler3::OnAB, &muler, std::placeholders::_1, std::placeholders::_2));
  subj.Notify(1, 2);
  return 0;
}