On 01/08/2006 04:37 AM, Ion Gaztañaga wrote: [snip]
types to call that constructor. What I would propose is the possibility of selecting via integer value which member of boost::variant will be constructed, just like which() returns the index of constructed member. This way, we can efficiently compact members of classes.
class MyRWLock { public: enum { r_prioriy, w_prioriy, a_prioriy };
MyRWLock(int run_time_policy);
private: struct r_prioriry_members { //... }; struct w_prioriry_members { //... }; struct a_prioriry_members { //... };
//Union of needed members boost::variant<r_prioriry_members, w_prioriry_members, a_prioriry_members> m_data; };
inline MyRWLock::MyRWLock(int run_time_policy) : m_data(/*what do I have to do to select a constructor?*/) {
}
[snip] Wizofaus had a somewhat similar problem which he posted here: http://tinyurl.com/dq732 In summary, he wanted a run time integer index to select a constructor to create some element of a variant. A solution posted in http://boost-consulting.com/vault/ under: Template Metaprogramming/little.funvec_.zip(little.funvec_foreach.cpp) uses a static constant vector of function pointers: setter_rec<RecId>::prp_vec_ctor const setter_rec<RecId>::our_prp_vec; which was used in: setter_rec<RecId>::set(void*in,int prop,int value) { our_prp_vec[prop](in,value); } The above set corresponds to your runtime selection of the ctor from a vector of "pseudo" ctor's stored in our_prp_vec. The void*in corresponds to your &m_data. The above value argument would not be needed since the "pseudo" ctor's in our_prp_vec would supply the required arguments while invoking a placement new on &m_data. I've got something almost like this on my local machine. It's a successor to the boost sandbox boost/indexed_types. Let me know if you're interested.