class A {}
A a;
type_info info = typeid (a); // error type_info is private
i want a list list<type_info> to store the type of classes. Is there a solution?
views:
235answers:
3
+2
A:
You cannot instantiate objects of the type_info class directly, because the class has only a private copy constructor. Since the list needs copy constructor...
If you really need it, use std::list< type_info*>.
I don't know why you need this list, but I would think to an alternative design, not involving RTTI, if possible.
Cătălin Pitiș
2009-10-16 13:09:02
actually my intent is to make a map<typeinfo, typeinfo>. Given a typeinfo instantiating another type.sample usage :Get(typeof(PageA)) gives me a StyleA class
jack london
2009-10-16 13:17:28
Then you should really use someting like class ids which you create yourself.
Simon H.
2009-10-16 13:19:54
If you know that you're dealing with PageA's at compile time, you should put a typedef inside PageA. Example: class PageA { public: typedef StyleA style_t; //.... };Then when you want to instantiate the appropriate Style, you just do: "PageA::style_t mystyleinstance;".
Joseph Garvin
2009-10-16 14:01:40
I seem to remember getting typeid for non-polymorphic types just OK (including built-ins). Of course, I don't see how one would use such a map to instantiate anything. I think OP might also look into the factory patterns.
UncleBens
2009-10-16 17:59:06
The "only for polymorphic" part is not true. 'type_info' is generated for all types. No exceptions. The only thing that is specific for polymorphic types is that for polymorphic types 'typeid' will identify *dynamic* type of the object, while for non-polymorphic other types it describes *static* type of the object. "Enabling/disabling RTTI" is a compiler-specific feature, that doesn't exist at the language level. Normally, disabling RTTI will simply make 'typeid' return static type for polymorphic classes.
AndreyT
2009-10-16 18:15:50
You're right. My mistake. Updated
Cătălin Pitiș
2009-10-16 19:14:02
+1
A:
You can't create copies of 'type_info' objects. However, the result if 'typeid' is an Lvalue and the corresponding 'type_info' objects, once obtained, continue to live till the end of the program. For these reasons, you can safely store pointers to 'type_info' objects in your list.
AndreyT
2009-10-16 13:42:42
A:
From your comment to Cătălin Pitiș' answer, I understand that your goal is to write a function that returns a different "Style" type for different "Page" types. Does this have to be dynamic? If not, would something like this do what you want?
template<class PageT>
struct StyleOf;
template<>
struct StyleOf<PageA>{
typedef StyleA type;
};
template<>
struct StyleOf<PageB>{
typedef StyleB type;
};
// etc...
template<class PageT>
typename StyleOf<PageT>::type
GetStyle(const PageT&){
return StyleOf<PageT>::type();
}
Or, with Boost.MPL:
using boost::mpl::map;
using boost::mpl::pair;
typedef map<
pair<PageA, StyleA>,
pair<PageB, StyleB>,
//etc.
>
PageToStyle;
Getting the Style type from the Page type is:
boost::mpl::at<PageToStyle, Page>::type;
Éric Malenfant
2009-10-16 19:27:47