Boost.Any

支持类型安全地存储和获取任意类型的值

#include <list>
#include <boost/any.hpp>
#include <string>
#include <iostream>

typedef std::list<boost::any> many;

void append_int(many & values, int value)
{
  boost::any to_append = value;
  values.push_back(to_append);
}

void append_string(many & values, const std::string & value)
{
  values.push_back(value);
}

void append_char_ptr(many & values, const char * value)
{
  values.push_back(value);
}

void append_any(many & values, const boost::any & value)
{
  values.push_back(value);
}

void append_nothing(many & values)
{
  values.push_back(boost::any());
}


bool is_empty(const boost::any & operand)
{
  return operand.empty();
}

bool is_int(const boost::any & operand)
{
  return operand.type() == typeid(int);
}

bool is_char_ptr(const boost::any & operand)
{
  try
  {
    boost::any_cast<const char *>(operand);
    return true;
  }
  catch(const boost::bad_any_cast &)
  {
    return false;
  }
}

bool is_string(const boost::any & operand)
{
  return boost::any_cast<std::string>(&operand);
}

void count_all(many & values, std::ostream & out)
{
  out << "#empty == "
    << std::count_if(values.begin(), values.end(), is_empty) << std::endl;
  out << "#int == "
    << std::count_if(values.begin(), values.end(), is_int) << std::endl;
  out << "#const char * == "
    << std::count_if(values.begin(), values.end(), is_char_ptr) << std::endl;
  out << "#string == "
    << std::count_if(values.begin(), values.end(), is_string) << std::endl;
}

int main()
{
  many values;

  append_int(values, 3);
  append_any(values, 4);
  append_char_ptr(values, "abc");
  append_string(values, std::string("abc"));
  append_int(values, 5);
  std::string str = "def";
  append_string(values, str);
  append_any(values, str);
  append_nothing(values);

  count_all(values, std::cout);
  return 0;
}