[SAGA-RG] Semantics of the ns_entry constructor

[Ceriel Jacobs]

Andre Merzky wrote:
> Quoting [Ceriel Jacobs] (Aug 17 2009):
>> Andre Merzky wrote:
>>
>>> You are right: open should be able to open entries and
>>> directories (which *are* entries).  open_dir should work
>>> only for directories.  Same holds then indeed for the entry
>>> and dir constructors.
>> Are you sure? I have an issue with what you are saying about the
>> entry constructor. I think that if a ns_entry object represents
>> a directory, it should in fact be a ns_directory object.
> 
> Well, directory inherits entry, so you can alw2ays do:
> 
>   saga::url         u ("file://localhost/etc/")
>   saga::file::dir   d (u);
>   saga::file::entry e = d; // downcast should always work

Yes, but upcast does not. My point is that the ns_entry constructor
cannot create a ns_directory. It is a constructor, after all.

> If the above works, I don't see why 
> 
>   saga::file::entry e (u);
> 
> should not work.  Or am I missing something?  The same then
> also holds for the open methods - the origin of Matijs'
> complain.

It is a major semantics change. If you do that, all methods in the
ns_entry implementations now have to consider the possibility that
the entry in fact is a directory, whereas earlier they could just
be hidden by ns_directory implementations. Also, I think it is confusing
that you can have a ns_entry object that represents a directory but cannot
be casted to a ns_directory. Note that I don't have an issue with the
change in the ns_directory.open method, only with the change in the ns_entry
constructor which, being a constructor, cannot deliver a ns_directory.

Cheers,		Ceriel