bug#5042: 23.1; linum-mode gives incorrect line numbers with narrowed buffers

[Drew Adams]

> Drew wrote:
> >  > > there should be an explicit option to switch between the modes.
> >  
> >  Yes, an option makes sense.
> >  
> >  And it can happen that the same person wants both behaviors at
> >  different times.  For that, why not let `C-u linum-mode' use, in
> >  effect, the opposite of the option value?
> 
> That might be a good idea.  Would an absolute override be better
> than a toggle?  E.g., a positive prefix uses absolute and a negative
> prefix uses relative to start of restriction.

I don't think so. Given the option's value, there already is a default behavior,
which makes one of your cases unnecessary. IOW, there is no override for one of
the two possibilities - the default behavior already corresponds to the
requested one.

If a given user prefers, in general, to use absolute numbering or relative
numbering, then s?he would set the option to reflect that. Then s?he need only
use `C-u' for the minority of times when s?he wants the alternative behavior.

FWIW, I do this kind of thing in some of my own code. Given the ability to
customize the default behavior, I see no reason for also being able to specify
the _default_ behavior explicitly via a particular prefix arg.

If, on the other hand, you were anticipating non-interactive use, then I'd say
that in that case all that's needed is to let-bind the variable (option) to give
it the value you want currently.