If the Daf repository is persistent (resides on disk), returns the absolute path leading to it. If the repository is (at least partially) in-memory, returns NULL.
Value
A character string with the absolute path to the persistent Daf repository, or NULL if the repository is in-memory.
Details
The returned path can be given to complete_daf to access the repository
after the current process is terminated. Note that for H5df format, the path may
end with #... to identify a specific group inside an HDF5 file.
See the Julia documentation for details.