loki仿函数原理

loki仿函数原理

问题一：已知函数Fun有2个参数，请完成CTestFunctor类，使得CTestFunctor的()实际调用Fun，部分代码如下：

#include <iostream>

using namespace std ;

class CTestCommand
{
public:
 void operator()(int x,double y)
 {
  cout << "CTestCommand的operator" << x << " " << y << endl;
 }
};

void Fun(double x,int y)
{
 cout << "全局函数" << x << " " << y << endl;
}

void main()
{
 CTestCommand cmd ;
 CTestFunctor<CTestCommand,void,int,double> f(cmd);
 f(3,4.5);

CTestFunctor<void (*)(double,int),void,int,double> f2(Fun);
 f2(100,1000);
}

参考答案：
template<typename FNU,typename R,typename P1,typename P2>
class CTestFunctor
{
public:
 CTestFunctor(const FNU& fun):m_fun(fun)
 {
  
 };
 R operator()(P1 p1,P2 p2)
 {
  return m_fun(p1,p2);
 }
protected:
 FNU m_fun;
};
 
问题二，参数类型不定，但不超过5个。
#include <iostream>

using namespace std ;

class CTestCommand
{
public:
 void operator()()
 {
  cout << "无参数" << endl ;
 }
 void operator()(int x )
 {
  cout << "1参数" << endl ;
 }
 int operator()(double x,int y)
 {
  cout << "2参数" << x << " " << y << endl;
  return 2;
 }
 void operator()(char x,char y ,char z )
 {
  cout << "3参数" << x <<" " << y << " " << z << endl ;
 }
 void operator()(short x,short y,short z,short w)
 {
  cout << "4参数" << x <<" " << y << " " << z << " " << w << endl ;
 }
 void operator()(short x,short y,short z,short w,short v)
 {
  cout << "5参数" << x <<" " << y << " " << z << " " << w << " " << v << endl ;
 }
};

class NullType
{
 NullType();//构造函数只有声明，没实现，所以不会被调用
};
 
template<typename FNU,typename R,typename P1=NullType,typename P2=NullType,typename P3=NullType,typename P4=NullType,typename P5=NullType>
class CTestFunctor
{
public:
 CTestFunctor(const FNU& fun):m_fun(fun)
 {
  
 };
 R operator()()
 {
  return m_fun();
 };
 R operator()(P1 p1)
 {
  return m_fun(p1);
 };
 R operator()(P1 p1,P2 p2)
 {
  return m_fun(p1,p2);
 };
 R operator()(P1 p1,P2 p2,P3 p3)
 {
  return m_fun(p1,p2,p3);
 };
 R operator()(P1 p1,P2 p2,P3 p3,P4 p4)
 {
  return m_fun(p1,p2,p3,p4);
 };
 R operator()(P1 p1,P2 p2,P3 p3,P4 p4,P5 p5)
 {
  return m_fun(p1,p2,p3,p4,p5);
 };
protected:
 FNU m_fun;
};

void main()
{
 CTestCommand cmd ;
 CTestFunctor<CTestCommand,void> f0(cmd);
 f0();

CTestFunctor<CTestCommand,void,int> f1(cmd);
 f1(1);

CTestFunctor<CTestCommand,int,double,int> f2(cmd);
 int x = f2(1,2);

CTestFunctor<CTestCommand,void,char,char,char> f3(cmd);
 f3(1,2,3);

CTestFunctor<CTestCommand,void,short,short,short,short> f4(cmd);
 f4(1,2,3,4);

CTestFunctor<CTestCommand,void,short,short,short,short,short> f5(cmd);
 f5(1,2,3,4,5);
}

问题三：
假定有默认值。
CTestCommand改成如下：
class CTestCommand
{
public: 
 void operator()(short x=1,short y=2,short z=3,short w=4,short v=5)
 {
  cout << "5参数" << x <<" " << y << " " << z << " " << w << " " << v << endl ;
 }
};

f2改成如下：
CTestFunctor<CTestCommand,int,double,int> f2(cmd);
 f2(1,2);
运行正常。

问题四：
看看容错性如何？
class CTestCommand
{
public: 
 void operator()(short x,short y)
 {
  cout << "5参数" << x <<" " << y  << endl ;
 }
};
假定少一个参数，我们看会报错吧。
void main()
{
 CTestCommand cmd ;
 CTestFunctor<CTestCommand,void,short> f1(cmd);
 f1(1); 
}
报错。
void main()
{
 CTestCommand cmd ;
 CTestFunctor<CTestCommand,void,short,short> f1(cmd);
 f1(1); 
}
报错
void main()
{
 CTestCommand cmd ;
 CTestFunctor<CTestCommand,void,short> f1(cmd);
 f1(1,2); 
}
报错。
编译器，就可以发现参数不一致的错误。