Re: [Boost-users] seeking comments on 'weak_key_map' experiments

AMDG Nicolas Lelong wrote:

I've been doing too much Python recently - thanks to boost.python - and my return in the c++ world in quite painful. To help me manage some of my objects lifetime dependencies, I wanted an access to a system similar to the Python WeakKeyDictionary class :

Mapping class that references keys weakly. Entries in the dictionary will be discarded when there is no longer a strong reference to the key. This can be used to associate additional data with an object owned by other parts of an application without adding attributes to those objects.

I drafted a small 'weak_key_map' class based on boost weak_ptr, shared_ptr deleters, and a base class enabling classes to be used as keys in the weak_key_map.

A small use case example is shown after, and source of weak_key_map & co are attached.

I was wandering if someone had experience to share about a similar system ?

For a first draft, it already serves me well - but, I'm not very happy with to "pollute" keys with the base class 'enable_master_ptr'...

Any idea to improve all this ?

Is there some way that this can interface with boost::shared_ptr/weak_ptr better? weak_key_map m; boost::shared_ptr<int> k(new int(1)); m.insert(std::make_pair(k,5)); assert(*m.find(k) == 5); k.reset(); assert(m.empty()); I rather suspect that the data structure would need to be implemented from scratch. One of the nastier problems is how to deal with the case of: iterator invalidation. The safest solution is to make the presence of an iterator to a particular element guarantee that the key continues to exist. struct node { boost::weak_ptr<K> key; V value; node* parent; node* left; node* right; }; struct iterator { boost::shared_ptr<K> key; // force the key to stay alive node* pos; }; In Christ, Steven Watanabe