I vote for flyweight to be accepted into boost. Earlier this week I have tried to plug a flyweight<string> type into Boost.Wave but failed at doing so for reasons related to Boost.Wave or my inexperience with Boost.Wave. So this review is based on a look at its implementation and a longer look at its documentation. I am knowledgable about the domain as I have implemented my own flyweight type which was only customizable in respect to the parameters for the hash container and which used a refcount tracking. First of all I don't mind the name factory but I would prefer flyweight_pool. I think the design is very good and the amount of work that Joaquin has done for a seemingly simple library is amazing. The documentation is very detailed minus some minor spelling errors. It could use a better example in the Introduction with a custom object and a custom hash function. Because 'how do I use boost.hash again' was the question in my head. As was already mentioned, a way to get usage statistics about the flyweights would be nice. Kevin