Re: [Boost-users] boost::any and const pointers

2 Dec 2009


      AMDG

James C. Sutherland wrote:
...
I have a 
  map
that I would like to control access to so that if a pointer is put in the map, only a const pointer can be extracted.  The following simple code illustrates the situation.
//-------------------- <snip> --------------------------
typedef std::mapstd::string,boost::any Properties;
template<typename T>
void
set( Properties& p, const std::string name, const T t )
{
  p[name] = t;
}
template<typename T>
const T
get( const Properties& p, const std::string name )
{
  const Properties::const_iterator iprop=p.find(name);
  try{
    const T t = boost::any_cast<const T>(iprop->second);
    return t;
  }
  catch(const boost::bad_any_cast &){
    throw std::runtime_error("bad cast");
  }
}
int main()
{
  Properties p;
  int i=1;
  set(p,"int",i);
  set(p,"int*",&i);
int*       j = get(p,"int*");  // I don't want this to compile
  const int* k = get(p,"int*");  // I want this to compile fine.
}
//-------------------- </snip> -------------------------
Currently this whole code compiles without trouble, but I don't want to allow a non-const pointer to be extracted.  Any ideas of how to accomplish this?
template<typename T>
const typename boost::remove_pointer<T>::type*
get(const Properties& p, const std::string& name);

In Christ,
Steven Watanabe