[cpp]: 获取“实例对象”--template 编程

[cpp]:   获取“实例对象”--template 编程

 

 

 

 

一、代码

#include <iostream>
#include <string>


using namespace std;


class base { };


class work:base {
public:
    work(){}
    work(string s1, string s2){}
    work(string nc, string s1, string s2){  }
    string get_type(){ return type; }
private:
    string type = "work";
};

    
class book:base{
public:
    book(){}
    string get_type(){ return type; }
private:
    string type = "book";
};


    
    
/****  important: begin  *****/ 


// return object of type 'work'
work
set_class(string s1, string s2)
{
    return work(s1,s2);
}


// return object of type 'T'; general program;
template<class T, class ...U>
T
get_object(U ...u)
{
    return T();
}


/****  important: end  *****/ 




// systhesis
void run()
{
    string s1="hello";  string s2="world";
    
    cout << s1 << ", " << s2 << endl;
    
    cout << "object0_type := " << set_class(s1,s2).get_type()  << endl;
    
    cout << "object1_type := " << get_object<work, string>(s1).get_type() << endl;
    
    cout << "object2_type := " << get_object<work, string>(s1,s2).get_type()  << endl;
    
    cout << "object3_type := " << get_object<book>(1).get_type()  << endl;
    
    cout << "object4_type := " << get_object<book>(1, 'c').get_type()  << endl;
    
    cout << "object5_type := " << get_object<book>(1, 'c', "string").get_type()  << endl;
    
    cout << "object6_type := " << get_object<book>(1, 'c', 3.14, "string").get_type()  << endl;  
}


// test part; entrance
int main()
{
    run();
    
    return 0;    
}

 

 

 

 

二、运行结果

g++ -std=c++20 -O2 -Wall -pedantic -pthread main.cpp && ./a.out

hello, world
object0_type := work
object1_type := work
object2_type := work
object3_type := book
object4_type := book
object5_type := book
object6_type := book

 

 

 

 

三、参考资料：

 

　　1、parameter pack    --    https://en.cppreference.com/w/cpp/language/parameter_pack

 

　　2、Template parameters and template arguments  --    https://en.cppreference.com/w/cpp/language/template_parameters#Type_template_parameter