Effective C++ 35：考虑虚函数的其他替代设计

https://github.com/wangcy6/weekly/blob/master/reading-notes/STL%E6%BA%90%E7%A0%81%E5%89%96%E6%9E%90/stl.md

// comparator predicate: returns true if a < b, false otherwise
struct IntComparator
{
  bool operator()(const int &a, const int &b) const
  {
    return a < b;
  }
};

https://github.com/wangcy6/weekly/tree/master/reading-notes/object-model

class NewCalcuClient
{
private:
    std::function<int(int, int)> m_function;

public:
    NewCalcuClient(std::function<int(int, int)> function) : m_function(function){}

    int calculate(int x, int y)
    {
        return m_function(x, y);
    }
};

Minus minus;
    CalcuClient client(&minus);

    Plus plus;
    CalcuClient client2(&plus);

    int r = client.calculate(7, 4);
    int r2 = client2.calculate(7, 4);

　　 //bind+function
    NewCalcuClient newclient(boost::bind(&Minus::calculate, &minus, _1, _2));
    NewCalcuClient newclient2(boost::bind(&Plus::calculate, &plus, _1, _2));

    int r3 = newclient.calculate(7, 4);
    int r4 = newclient2.calculate(7, 4);