Bug#465140: debian-policy: clarify when to use alternatives

[Ian Jackson <ian@davenant.greenend.org.uk>]

David Paleino writes ("Bug#465140: debian-policy: clarify when to use alternatives"):
> Please specify "same API" as well as "same functionality".

update-alternatives is usually used for commands which might be used
by end users at the command line, and we don't require them to be
identical.

We just require that there be some common idea of what interface can
be relied on by things which use the varying name.

> A discussion [1] on debian-devel about libtranslate-bin and
> translate suggested that alternatives should be used only when, in
> case of libraries, the same API is provided, no matter if they offer
> more or less the same functionalities.

I don't think the alternatives system is a good answer for libraries
and it probably shouldn't be used for that.

If nothing else, you'd have to coordinate changes to headers and
.so/.a files and it would get quite out of hand.

The usual approach here has been either conflicting packages, or
coinstallable packages which the depending package explicitly selects
between.

Ian.