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

Subject: Re: [boost] [BGL] [PropertyMap] Key param is passed by value in put function
From: Cosimo Calabrese (cosimo.calabrese_at_[hidden])
Date: 2009-11-18 06:28:26

Cosimo Calabrese wrote:
> 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;
>   }
> 

The same thing is in class iterator_property_map, in operator[] the key 
value is passed by value:

inline R operator[](key_type v) const { return *(iter + get(index, v));}

Best regards,
Cosimo Calabrese.