Phoenix 3.0.4 is now on master and will I hope be included in the next release of Boost. There are many fixes to bugs which are documented in libs/phoenix/ChangeLog In particular there are fixes for #5715 and #5824. These are important as they were silent bugs which meant that code did not work correctly. This means that it is possible that there is code using phoenix where the results could change when adopting this release. There are many fixes still to be done which are documented in the TODO section of the changelog. Please report any concerns or bugs either through trac or by responding to this message. John Fletcher