Re: (concat "/dir/name/" "foo") --> (expand-file-name "foo" "/dir/name/")

[prj@po.cwru.edu (Paul Jarc)]

Kai.Grossjohann@CS.Uni-Dortmund.DE (Kai Großjohann) writes:
> On 22 Oct 2000, Paul Jarc wrote:
> > A mischevious, badly-written, or maybe just an unconventional
> > handler might give an expanded name that would, when re-expanded,
> > give a different name.  But this probably doesn't happen in most
> > normal situations.
> 
> So it's a bug when expand-file-name fails to be idempotent?

In such a case, it's a bug to expand an already-expanded name, yes.  I
don't know whether any code actually has this bug.

> Hm.  Maybe it isn't too bad after all, but one has to be very careful
> to say (concat (file-name-as-directory D) F), not just (concat D F).
> But I think you were saying that file-name-as-directory might not be
> idempotent, either, right?  So we have just shifted the problem.

True, if you don't know whether D is as-directory to begin with.  But
expand-file-name does other things as well; file-name-as-directory
does only one simple thing, so it has a better chance of being
idempotent, even if only by accident.


paul