C++中function的实现原理详解

#include <iostream>
#include <string>
using namespace std;

template<typename T>
class MyFunction3 {

};

template<typename Ty, typename A1>
class MyFunction3<Ty(A1)> {

public:
	typedef Ty(*pFunction)(A1);//定义一个函数指针,指针指向的函数返回类型是Ty,有1个函数参数
	MyFunction3<Ty(A1)>(pFunction _pFunction) : _function(_pFunction) {
	}

	Ty operator()(A1 arg1) {
		return (*_function)(arg1);
	}

private:
	pFunction _function;
};


template<typename Ty,typename A1,typename A2>
class MyFunction3<Ty(A1,A2)> {

public:

	typedef Ty(*pFunction)(A1, A2);//定义一个函数指针,指针指向的函数返回类型是Ty,有两个函数参数
	MyFunction3<Ty(A1, A2)>(pFunction _pFunction):_function(_pFunction) {
	}
    
	Ty operator()(A1 arg1, A2 arg2) {
		return (*_function)(arg1, arg2);
	}

private:
	pFunction _function;
};


void showMes(string mes) {
	cout << "showMes(string mes)=" << mes << endl;
}


int sum1(int x, int y) {
	cout << "sum1 "<<(x+y) << endl;
	return x + y;
}
int sum2(int x, int y) {
	cout << "sum2 " << (x + y) << endl;
	return x + y;
}

int main() {

	MyFunction3<int(int, int)> f1(sum1);
	f1(20,30);


	MyFunction3<void(string)> f2(showMes);
	f2("AAAA");

	system("pause");
	return 0;
}

#include <iostream>
#include <string>
using namespace std;

template<typename T>
class MyFunction4 {

};


template<typename R , typename... A >
class MyFunction4<R(A...)> {

public:
	typedef R(*PFUNCTION)(A...);

	MyFunction4<R(A...)>(PFUNCTION _p) : function(_p) {}

	R operator()(A... arg) {
		return (*function)(arg...);
	}

private:

	PFUNCTION function;
};


void showMes1(string mes) {
	cout << "showMes(string mes)=" << mes << endl;
}

int sum11(int x, int y) {
	cout << "sum11 " << (x + y) << endl;
	return x + y;
}
int sum21(int x, int y) {
	cout << "sum21 " << (x + y) << endl;
	return x + y;
}

int main() {

	MyFunction4<int(int, int)> f1(sum11);
	f1(20, 30);


	MyFunction4<void(string)> f2(showMes1);
	f2("AAAA");

	system("pause");
	return 0;
}