[Boost-users] [multi_index] function object as key extractor?

From: Boris (boriss_at_[hidden])
Date: 2007-03-14 09:58:12

As I find myself replacing all kind of C++ standard containers with  
multi_index_container (a really very useful container) I've been defining  
key extractors quite a lot and wonder if there is any shortcut like using  
lambda expressions or function objects. Here's some pseudo-code to explain  
what I mean:

struct foo
{
        std::string s;
        foo(std::string s) : s(s) { }
};

typedef multi_index_container<
        foo,
        indexed_by<
                hashed_unique<
                        boost::bind<std::size_t, &std::string::size, member<foo, std::string,  
&foo::s> >
		>
	>
> mi_t;

The idea is to call another function on the object which is returned by  
the key extractor member. Here in this example the multi_index_container  
would only store strings with a unique size. However I'm lost how to  
define the key extractor. The difficulty is probably that I normally don't  
need to specify types when I use boost::bind or lambda expressions. Now I  
need to figure out how to use them with multi_index_container - is there  
any trick or I better go on defining key extractors?

Boris