Re: [Boost-users] Generic indexing by "const char *"

From: Joseph Fradley (joe.fradley_at_[hidden])
Date: 2008-01-29 13:42:22

Joseph Fradley wrote:
>
> I have a problem that I would like to solve in the most generic
> non-intrusive way possible (such as boost serialization). What I want
> is to access class members both via it's initially designed accessors
> but also via a "const char *"  key. In addition, I want to pass list
> of key's (via a vector of const char * or a single delimited multikey
> char *) to get nested member access.
>
> For example:
> ...
> // these should be equivalent
> Point p;
> int val;
> val = p.x;
> val = p.getX();
> p.getMemberValue("x", val);
>
> // there also
> Rectangle r;
> int val;
> Point pVal;
> r.getMemberValue("corner:x", val);
> r.getMemberValue("corner", pVal);
>

Steven Watanabe wrote:

>You could try something along these lines:
>
>class indexable_base {
>public:
>  virtual indexable_base* lookup(const char*) = 0;
>  virtual const std::type_info& get_type() = 0;
>    virtual void* get() = 0;
>};
>
>Then you can put macros in the derived class like so:
>
>class Rectangle : public indexable_base {
>   DEFINE_LOOKUP() {
>       DECLARE_VARIABLE(corner);
>   }
>   Point Corner;
>};
>
>Which would expand to something like
>
>class Rectangle : public indexable_base {
>   template<class T>
>   void getMemberValue(const char* key, T& out) {
>       indexable_base result = lookup(key);
>       if(typeid(T) == result->get_type()) {
>           out = *(static_cast<T*>(result->get()))
>       } else {
>           throw(std::bad_cast());
>       }
>   }
>   indexable_base* lookup(const char* key) {
>       // split key at ":" and lookup call lookup_ recursively until
>all the keys are used up.
>   }
>   static void init() {
>       map_.insert(std::make_pair("corner",
>&boost::bind(&Rectangle::corner, _1)));
>   }
>   Point corner;
>};
>

Steven,

Thank you, I'm trying it now. But I'm a confused as to what type of
map to create from your line :
   map_.insert(std::make_pair("corner", &boost::bind(&Rectangle::corner, _1)));

I've just now read up on boost::bind and I can only see documentation
of binding to member functions not member data. Could you elaborate?

Joe