boost::any 用法

// In header: <boost/any.hpp>


class any {
public:
  // construct/copy/destruct
  any();
  any(const any &);
  template<typename ValueType> any(const ValueType &);
  any & operator=(const any &);
  template<typename ValueType> any & operator=(const ValueType &);
  ~any();

  // modifiers
  any & swap(any &);

  // queries
  bool empty() const;
  const std::type_info & type() const;
};

#include <iostream>
#include <string>
#include <utility>
#include <vector>
#include "boost/any.hpp"

class A 
{
public:  
    void some_function() 
    { 
        std::cout << "A::some_function()\n"; 
    }
};
class B
{
public:  
    void some_function() 
    { 
        std::cout << "B::some_function()\n"; 
    }
};

void print_any(boost::any& a)
{  
    if (A* pA=boost::any_cast<A>(&a)) 
    {   
        pA->some_function();  
    }  
    else if (B* pB=boost::any_cast<B>(&a))
    {   
        pB->some_function();  
    }      
    else
    {   
        try 
        {     
            std::cout << boost::any_cast<std::string>(a) << ‘\n‘;   
        }   
        catch(boost::bad_any_cast&) 
        {     
            std::cout << "Oops!\n";   
        }  
    }
}

int main() 
{  
    std::cout << "Example of using any.\n\n"; 
    std::vector<boost::any> store_anything;  
    store_anything.push_back(A());  
    store_anything.push_back(B());  
    // 我们再来，再加一些别的东西  
    store_anything.push_back(std::string("This is fantastic! "));  
    store_anything.push_back(3);  
    store_anything.push_back(std::make_pair(true, 7.92));     
    std::for_each(  store_anything.begin(),  store_anything.end(),  print_any);


     std::cout << "Example of using any member functions\n\n"; 
     boost::any a1(100); 
     boost::any a2(std::string("200"));  
     boost::any a3; 
     std::cout << "a3 is "; 
     if (!a3.empty()) 
     {    
         std::cout << "not empty\n "; 
     }  
     std::cout << "empty\n";  
     a1.swap(a2); 
     try 
     {   
         std::string s=boost::any_cast<std::string>(a1); 
         std::cout << "a1 contains a string: " << s << "\n"; 
     } 
     catch(boost::bad_any_cast& e) 
     {  
         std::cout << "I guess a1 doesn‘t contain a string!\n"; 
     } 
     if (int* p=boost::any_cast<int>(&a2)) 
     {  
         std::cout << "a2 seems to have swapped contents with a1: "      << *p << "\n"; 
     } 
     else
     {    
         std::cout << "Nope, no int in a2\n"; 
     }  
     if (typeid(int)==a2.type()) 
     {    
         std::cout << "a2‘s type_info equals the type_info of int\n";  
     }

}
 

2）解决类似与map但是可以映射到各种不同的类型的问题：

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include "boost/any.hpp"
class property
{  
    boost::any value_;
    std::string name_;
public:  
    property(const std::string& name,const boost::any& value)  
        : name_(name),value_(value) {}  
    std::string name() const { return name_; } 
    boost::any& value() { return value_; } 
    friend bool operator<(const property& lhs, const property& rhs)
    {return lhs.name_<rhs.name_;}
};
void print_names(const property& p) 
{ 
    std::cout << p.name() << "\n";
}
int main() 
{  
    std::cout << "Example of using any for storing properties.\n";
    std::vector<property> properties; 
    properties.push_back(  property("B", 30));
    properties.push_back(  property("A", std::string("Thirty something"))); 
    properties.push_back(property("C", 3.1415));  
    std::sort(properties.begin(),properties.end());
    std::for_each(properties.begin(),  properties.end(),  print_names);
    std::cout << "\n";  
    std::cout <<  boost::any_cast<std::string>(properties[0].value()) << "\n"; 
    std::cout <<  boost::any_cast<int>(properties[1].value()) << "\n"; 
    std::cout <<  boost::any_cast<double>(properties[2].value()) << "\n";    
}