The functional approach seems to work great for sandboxing binary artifacts of packages, but configuration files and user data are more difficult to handle. Daniel Burrows, a debian apt developer, wrote an analysis of Nix a while back[1], and he brought up the problematic example of upgrading database configuration file formats. It seems difficult to seamlessly upgrade and downgrade these types of files whose semantics and syntax may change between versions. When these conflicts occur in Debian/Ubuntu, the upgrade process blocks and the user is prompted to resolve the 3-way merge.
I think packakge managers should only handle the storage of static files like executables and shared libraries. Forcing the user or another process to handle configuration files and startup/shutdown hooks has additional benefits such as making these files easier to store in version control.
I think packakge managers should only handle the storage of static files like executables and shared libraries. Forcing the user or another process to handle configuration files and startup/shutdown hooks has additional benefits such as making these files easier to store in version control.
[1] http://lists.debian.org/debian-devel/2008/12/msg01027.html