[Distutils] Simple idea to resolve versioning problems

[Greg Ewing]

David Cournapeau wrote:
> Greg Ewing wrote:
>
> > If they really do need different versions, this is insoluble.
>
> But that's by far the most significant problem of packages with a lot of 
> dependencies !

But if your application really does depend on two libraries that
have conflicting requirements like this, the application itself
is screwed to begin with. There's *no* way of making it work
on *any* system, whether that system has library versioning or
not.

Consequently, the developer will be unable to make it work on
his own machine, and will therefore never attempt to deploy it!

> It is ok to have a few 
> major, side by side versions for fundamental packages (on my ubuntu 
> system, I do have system installed qt 3 and qt 4, for example). This 
> would be good to have in python, I agree.

That's what I'm talking about! As long as the API remains
backward compatible, there is no need to have anything but the
latest version installed -- and in fact, in the kind of system
I have in mind, the earlier versions would *never be used*
even if they were installed.

That's because the program would say something like "Please
give me gtk-2.3", and the system would know that anything
called gtk-2.x with x >= 3 is compatible with that, and would
pick the one with the greatest x out of those available.

However, if a gtk-3.0 ever comes out, it implies that the
API is *not* backward compatible. So then it makes sense to
have both a gtk-2.x and a gtk-3.y installed, and the versioning
system will keep them from getting confused.

This relies on a couple of things: (a) library developers
sticking rigidly to the version numbering semantics; (b)
applications always requesting the version they actually
require.

> IOW, enabling version requirement without strong API compatibility is 
> the path to dependency hell.

I fully agree. However, this is a social issue, not a
technical one. Everyone using the versioning system would
need to understand the rules and be willing to follow them.

-- 
Greg