Re: Thoughts on Format

From: bill_kempf (williamkempf_at_[hidden])
Date: 2002-01-31 10:20:55

--- In boost_at_y..., "Brey, Edward D" <EdwardDBrey_at_e...> wrote:
> > From: bill_kempf [mailto:williamkempf_at_h...]
> > 
> > My own opinion is that generalized formatting is already handled 
> > quite nicely by iostream manipulators any way (the only two 
arguments 
> > I've ever heard against this was that "printf" was more 
intuitive, 
> > which is true only for old C coders, and that the manipulator 
> > approach was very verbose, but I could care less about that).
> 
> Verbosity does make a difference.  Fortunately, the difference can 
be
> explained in terms other than the nebulous "intuition factor" or
> "convenience factor".
> 
> It's a matter of engineering principle: locality of reference, as 
applied to
> its impact on the programmer.  With the printf-style, you get good 
locality
> of the format text:
> 
> "Task [1] will complete within [2] second(s)."

This is *NOT* printf-style formatting.  This is solely syntax for 
positional parameters, which I very strongly support.  (And I could 
care less if the delimiter string syntax is %1%, %1$, [1], (1), %001 
or any other variant you want to throw at it.)

What I don't like is any attempt to retain printf's type specifiers 
and to a large degree attempts to retain length, precision, etc. 
specifiers.

> That is to say, it is easy to see the flow of the sentence, the 
correlation
> between "Task" and "will complete", for example.
> 
> With stream style, you get good locality of the variables to their
> surrounding text:
> 
> "Task " << task_name << " will complete within " <<
>   estimated_completion_time - current_time() << " second(s)."
> 
> Here it is easy to pair "Task" and "task_name", for example.
> 
> Each type of locality has its own advantage.  There is a tradeoff, 
and which
> style is best depends on the situation.  In my experience, I've 
found that
> when dealing with full English sentences, the locality of the 
format context
> is most desirable, whereas for short, simple outputs, like those in 
some
> trace logs, locality of a variable to its text is most desirable.

When speaking of locality, to me the important thing is to keep the 
formatting code with the object being formatted.  In other words, I 
think that:

cout << format("[1]") << width(10) << foo;

is much preferrable to:

cout << format("[1:10]") << foo;

I think it's easier to read and comprehend, and it certainly will 
make the translation of the format string easier.

Bill Kempf