[boost] [BGL] [PropertyMap] Key param is passed by value in put function

Subject: [boost] [BGL] [PropertyMap] Key param is passed by value in put function
From: Cosimo Calabrese (cosimo.calabrese_at_[hidden])
Date: 2009-11-18 05:59:20

Hi to all,

I've noticed that the put function that takes a generic put_get_helper 
map, takes a key param. The question is: why the key param is passed by 
value? Is any reason for this? The key value is not modified setting the 
property map.

I've noticed it because in my graph type the descriptors are variant, 
and so every time I've to set a property map, a new copy of the variant 
is created.

I've reported the function below, for sake of comfort. It is in 
boost/property_map.hpp

   template <class PropertyMap, class Reference, class K, class V>
   inline void
   put(const put_get_helper<Reference, PropertyMap>& pa, K k, const V& v)
   {
     static_cast<const PropertyMap&>(pa)[k] = v;
   }

Best regards,
Cosimo Calabrese