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Boost.Flyweight Future work

New functionalities can be included into future releases of Boost.Flyweight to meet the demands of users and to leverage upcoming C++0x features and new Boost libraries. The following is a list of candidate additions.


Introspection API

Currently there is no way to access the internal components of a flyweight instantiation (factory, holder, etc.) or even to know the types of these components. With such an API it would be possible to instrument and monitor the usage of Boost.Flyweight like in the following example:

typedef flyweight<std::string> fw_type;
std::cout<<"factory used:  "<<typeid(fw_type::factory_type).name()<<std::endl;
std::cout<<"values stored: "<<fw_type::factory().size()<<std::endl;

Perfect forwarding

When constructing a flyweight<T> object, some spurious copies of objects of type T are incurred in the process of moving the value into the internal factory. So-called perfect forwarding, i.e. performing the move without generating temporary copies, will be solved in an optimum manner by a new type of rvalue references to be included in the next revision of the C++ standard. Boost.Flyweight will take advantage of this feature as compilers begin to provide it.

Read/write locking policy

The nature of the flyweight pattern implies that most accesses to the internal flyweight factory do not cause new insertions and can thus be considered read-only. This hints at the convenience of using a locking policy based on read/write locks such as those provided by Boost.Thread. Implementing a locking policy will also require extending the Factory concept to allow for pure lookup operations. Tim Blechmann has provided a preliminary implementation of this idea. Before committing to this library extension it is necessary to do a profiling study to determine whether read/write locking actually improves performance.

Integration with new Boost libraries

Recently accepted Boost libraries like Boost.Functional/Forward and Boost.Functional/Factory might be used in the future to replace some internal machinery of Boost.Flyweight.

Revised September 1st 2008

© Copyright 2006-2008 Joaquín M López Muñoz. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at