function bind

reference

http://blog.bitfoc.us/p/525

STL 源码简析 – std::function

Naive std::function implementation

step1 匹配函数

#include <iostream>
using namespace std;

template <typename T>
struct function{};

template <typename ret, typename lhs, typename rhs>
struct function<ret(lhs, rhs)>
{
    enum {values = 2};
};

int func(int, int)
{
    cout << "func ..." << endl;
}

int main()
{
    cout << function<int(int, int)>::values << endl;    //2
}

step2 模板匹配分析

#include <iostream>
using namespace std;

template <typename T>
struct function{};

template <typename ret, typename lhs, typename rhs>
struct function<ret(lhs, rhs)>
{
    static const int values1 = std::is_same<int, ret>();
    static const int values2 = std::is_same<int, lhs>();
    static const int values3 = std::is_same<int, rhs>();
};

int func(int, int)
{
    cout << "func ..." << endl;
}

int main()
{
    cout << function<int(int, int)>::values1 << endl;   //1
    cout << function<int(int, int)>::values2 << endl;   //1
    cout << function<int(int, int)>::values3 << endl;   //1

    cout << function<double(int, int)>::values1 << endl;    //0
    cout << function<int(double, int)>::values2 << endl;    //0
    cout << function<int(int, double)>::values3 << endl;    //0
}

step3 运行函数

#include <iostream>
using namespace std;

template <typename T>
struct function{};

template <typename ret, typename lhs, typename rhs>
struct function<ret(lhs, rhs)>
{
    using functype = ret (*)(lhs, rhs);
    functype callfunc;

    template<typename T>
    function(T param):callfunc(param){

    }

    ret operator()(lhs l, rhs r){   //函数调用运算符
        return callfunc(l, r);
    }
};

int func(int lhs, int rhs)
{
    cout << "func ..." << endl;
    cout << lhs + rhs << endl;
}

int main()
{
    function<int(int, int)> test = &func;
    test(1, 2);
}

ending