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

2 Dec 2009


      On Dec 2, 2009, at 2:19 PM, Steven Watanabe wrote:
...
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
Thank you!
That works great for pointers, but now not for POD, e.g.,
	const int m = get<int>(p,"int");
Any ideas of how to get this to work with POD and pointers?