Re: [boost] [Filesystem] behaviour of branch_path

From: Beman Dawes (bdawes_at_[hidden])
Date: 2004-02-20 16:24:06

At 10:48 PM 1/25/2004, Gustavo Guerra wrote:

 >Why does branch_path return path("") with simple paths like "file.ext"?
 >Would'nt it make more sense to return path(".")? At least that was I was
 >expecting. I had to go carefully see at documentation to discover it 
wasn't
 >like that, because in other place in the docs its writen "A non-empty 
path
 >is specified as a precondition because an empty path is almost certainly 
an
 >error".
 >
 >This way, for example, if I have some code that gets the parent directory
 >of a path and then uses that in other path operations, I'm forced to make 

 >special cases checking for has_branch_path, when if it returned "." it
 >would work better for most cases...

In thinking more about this need, it seems to me that changing 
path::branch_path() may not be the best approach. Class path member 
functions work only on the lexical representation of a path, regardless of 
the actual state of the external filesystem. The use cases I can think of 
usually need to look at the external filesystem. Also, The decomposition 
functions return elements of the path. It seems a bit surprising for a 
decomposition function to return "." when it is not an element of the path.

Perhaps the use cases you are running into would be better dealt with by 
new operational functions which do look at filesystem state. Two possible 
functions come to mind (subject to better naming):

   path directory_path_of_file( const path & ph );

      Throws: !exists(ph) || is_directory(ph)

      Returns:  branch_path(ph).empty() ? path(".") : branch_path(ph)

   path directory_path( const path & ph );

      Throws: !exists(ph)

      Returns: is_directory(ph) ? ph : directory_path_of_file(ph)

Thoughts?

--Beman