Re: [gobo-eiffel-develop] indenting text output filter

[Bernd S. <ber...@in...>]

At Thu, 24 May 2007 13:18:20 +0200,
Andreas Leitner wrote:
> KL_TEXT_OUTPUT_FILTER -- just having the forwarding bits, doing no
> transformation at all
> 
> KL_INDENTED_TEXT_OUTPUT_STREAM | _FILTER -- just containing the
> indentation bits
> 
> Your name is intuitive and conveys the idea very well though, so if we
> decide to hide the filtering metaphor, that's fine with me.

I fully agree, having the concept of output filter would be nice for
many applications. In the long run, might even consider building a
cluster of filters.

> > Or should the indentation facility be part of KI_TEXT_OUTPUT_STREAM
> > with an option to enable it or not? In fact we probably don't need
> > an option, the fact that `indent' is never called (and hence
> > `indentation' is kept to 0) should be enough. The questions are:
> > is it acceptable to add 2 attributes to class KI_TEXT_OUTPUT_STREAM,
> > and will the test to figure out that there is actually no indentation
> > to be printed be noticeable in terms of performance?
> 
> That would actually be nice, since you don't need to build a pipeline.
> On the other hand, I think a pipeline is quite intuitive and easy to
> build (once you know the pattern) and it spreads the functionality so
> that KI_TEXT_OUTPUT_STREAM itself is more easy to understand.

Hmm - I think we should keep interfaces small to make it easy to
implement new output streams. Blowing up interfaces with indentation
facilities seems wrong. Filters are the better way to go.
 
> > Note your implementation is not bullet-proof. It won't work if we
> > call `put_string' with an argument that contains newlines. Is that
> > acceptable? If yes, it should be clearly stated.
> 
> Yeah, that's a very good point. I made it a habit of never writing
> manifest newlines so it is not an issue. Processing `put_string' for
> newline is a potential performance problem. So I would opt for leaving
> it like it is. You are absolutely right though, we should state it in
> the header comment and maybe even in the indexing clause.

Best would be if we can toogle replacing newlines in strings with
'put_string' on- and off. Also, if it is off, do we need a
precondition in put_string to enforce that the string does not contain
newlines?

I would even vote for switching it on by default, because it is the
little more universal (though less efficient) choice.

Bernd