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

Subject: Re: [Boost-users] boost::any and const pointers
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-12-02 16:19:10

AMDG

James C. Sutherland wrote:
> I have a 
> 	map<string,any>
> 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::map<std::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<int*>(p,"int*");  // I don't want this to compile
>   const int* k = get<int*>(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