[TCLCORE] tip115: text widget 'chars' vs 'indices'

[Vince D. <vi...@sa...>]

After several useful pieces of feedback on tip115, I've made a few
modifications and adjustments (in particular, including smooth scrolling
in the tip).  I would certainly appreciate any continued feedback on the
new version of the tip.

In particular, however, there is one area that probably ought to be
resolved before the tip is ready for
voting/final-implementation/full-testing etc.  This is the issue of
'chars' vs 'indices'.  Historically it seems there has been little
distinction made between these two concepts.  This is really only a
problem in one area:

  .text get $idx "$idx +N chars"

does not necessarily return N characters since what the above code
actually means is to step forward N _index_positions_. If there are any
embedded images or windows, then fewer than N characters will be returned.

In itself this isn't a problem, except how does one count in terms of
actual characters?  The best I can think of, which already makes use of
some features of tip155 is:

  set n $N
  while {[.text count -chars $idx "$idx + $n chars"] != $N} {
     incr n
  }

(ok, this could be improved further, but the basic point is we need some
sort of iteration to determine something which the widget could very, very
easily tell us).

What would be nice would be to have both '+N chars' and '+N indices', but
this of course would break backwards compatibility.

So, any suggestions?

thanks!

-- Vince

<http://www.santafe.edu/~vince>