Re: STL map containing pointer_to_binary_function

From:
Barry <dhb52@126.com>
Newsgroups:
comp.lang.c++
Date:
Thu, 30 Aug 2007 09:52:38 +0800
Message-ID:
<fb57t7$e40$1@aioe.org>
Glennmac@gmail.com wrote:

Barry,

Thanks for the help. I have been working on a different method to do
this, but have hit the same results.

I have created a base class:

template <typename T>
class base {
public:
 base(T eval) :
  mValue(eval)
 {};

 virtual ~base() {};

 bool run(const string &actualValue) {
   runInternal(mValue, actualValue);
 }

protected:
 virtual bool runInternal(int v1, const string &v2) = 0;
 virtual bool runInternal(const string &v1, const string &v2) = 0;

protected:
 T mValue;
};

template <typename T>
class d1 : public base<T> {
public:
 d1(T eval) :
  base<T>(eval)
 {};

private:
 bool runInternal(int v1, const string &v2) {
  // convert string to int
  return v1 == v2;
 };

 bool runInternal(const string &v1, const string &v2) {
  return v1 == v2;
 };
};

As I am sure you can see, I can not create a map<string, base *>
because base needs a type at that point. Can I somehow use a template
function in the class and not a complete template class?

Basically I need to have a map of functions, classes whatever that
test <, > and == of a known value and actual value. They can be
strings, int, and doubles. Is this possible?


So don't have
template <class T>
class Base;

instead have
class Base {
public:
     virutal bool Compare(boost::any arg0, boost::any arg2) = 0;
};

template <class T, U>
class Child : public Base
{
// override Compare
// boost::any_cast to T and U with arg0 and arg1, then do the compare
};

the code can be like this:

#include <iostream>
#include <map>
#include <algorithm>
#include <string>
#include <sstream>

#include <boost/any.hpp>

class Base {
public:
     virtual bool Compare(boost::any const& arg0, boost::any const& arg1)
     {
         return false;
     }

     virtual bool Compare(boost::any const& arg)
     {
         return false;
     }

     virtual ~Base () { }
};

template <class T, class U>
class Child1 : public Base
{
public:
     Child1(U arg1) : arg1_(arg1) {}

protected:
     virtual bool Compare(boost::any const& arg0)
     {
         if (T const* pT = boost::any_cast<T>(&arg0))
         {
             if ((*pT) == arg1_) {
                 std::cout << "true" << std::endl;
                 return true;
             }
         }

         return false;

     }
private:
     U arg1_;
};

template <class T, class U>
class Child2 : public Base
{
protected:
     virtual bool Compare(boost::any const& arg0, boost::any const& arg1)
     {
         T const* pT = boost::any_cast<T>(&arg0);
         U const* pU = boost::any_cast<U>(&arg1);

         if (pT && pU)
         {
             if ((*pT) == (*pU)) {
                 std::cout << "true" << std::endl;
                 return true;
             }
         }

         return false;
     }
};

bool operator== (std::string const& lhs, int rhs)
{
     std::ostringstream oss;
     oss << rhs;
     return lhs == oss.str();
}

bool operator== (int lhs, std::string const& rhs)
{
     std::ostringstream oss;
     oss << lhs;
     return rhs == oss.str();
}

int main()
{
     std::map<std::string, Base*> Map;
     Map["test1"] = new Child1<int, int>(10);
     Map["test2"] = new Child1<int, std::string>("100");
     Map["test3"] = new Child1<std::string, int>(100);

     Map["test1"]->Compare(10);
     Map["test2"]->Compare(100);
     Map["test3"]->Compare(std::string("100"));

     Map["test4"] = new Child2<int, int>();
     Map["test5"] = new Child2<int, std::string>();
     Map["test6"] = new Child2<std::string, int>();

     Map["test4"]->Compare(10, 10);
     Map["test5"]->Compare(100, std::string("100"));
     Map["test6"]->Compare(std::string("100"), 100);

     for (std::map<std::string, Base*>::iterator it = Map.begin();
          it != Map.end(); ++it)
     {
         delete it->second;
     }
}

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