On Dec 2, 2009, at 11:24 AM, Dominique Devienne wrote:

On Wed, Dec 2, 2009 at 10:55 AM, James C. Sutherland wrote:

...

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. }

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?

Thanks not possible AFAIK. The first compiles alright, but will fail at runtime because the boost::any was constructed using a const int*. By design all extractions are checked at runtime only, and the typeid()/std::type_info of what you put in and what you try to get it as must be the same. Given your code, you can't even do get<int>(p, "int"), because a const int was put in, not an int (see your set() impl), and typeid(int) != typeid(const int). --DD

Actually, this runs just fine (at least on my mac running g++ 4.2.1). Also, the following compiles and runs fine: int m = get<int>(p,"int"); This is because you cannot force const semantics on a copy. I came up with a way to get const references out (using boost::ref), but can't get const pointers guaranteed. I fear that you are right about this not being possible.

On Wed, Dec 2, 2009 at 3:29 PM, James C. Sutherland < James.Sutherland@utah.edu> wrote:

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?

Why can't you use boost::enable_if and only enable the get<> template if the argument is const? This imposes the restriction that you actually invoke the get<> template as follows: const int m = get<const int>(p, "int"); const int* m2 = get(p, "int*"); but it still seems to work. Is this unsatisfactory for some reason? Zach

On Dec 2, 2009, at 3:03 PM, Steven Watanabe wrote:

AMDG

James C. Sutherland wrote:

...

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?

typename boost::mpl::eval_if::type

...

, boost::add_const<T> ::type

In Christ, Steven Watanabe

You can work magic! I suppose that I need to dig into MPL and the type_traits libraries in boost. template< typename T > typename boost::mpl::eval_if< boost::is_pointer<T>, boost::add_pointer< typename boost::add_const< typename boost::remove_pointer<T>::type >::type >, boost::add_const<T> >::type get( const Properties& p, const std::string name ) { ... } that did the job.