RE: [boost] Boost.Format syntax

From: Brey, Edward D (EdwardDBrey_at_[hidden])
Date: 2002-02-11 10:15:42

> From: James Kanze [mailto:kanze_at_[hidden]]

> |>  I agree with the desire for printf compatibility.  But trying to
> |>  find a nice syntax that allows it just isn't easy.  For example,
> |>  using the "%1$s" use mentioned above, what happens if the value
> |>  substituted is a string that the context string will make plural.
> |>  Its not pretty: format("%1$s %2$ss") [3] ["banana"].
> 
> But it doesn't occur in practice.  You can't just add an s to make a
> word plural.

You can given a suitable precondition. :-)  Yes, I agree, this example isn't
the best (although I've seen it, both with the precondition and with '(s)'.
The larger point is that there is a significant minority of times when this
happens.  Usually when adding tabs, newlines, percentages, and the like.
They all are a bit easier to read when a fully enclosed placeholder.  Short
of that, string concatenation helps, but it isn't quite as nice as an
enclose placeholder would be.

> |>  What harm is there in completely separating the printf 
> syntax into a
> |>  different class?  Is there really any desire to use 
> (pseudo-)printf
> |>  syntax and a modern syntax within the same format object?
> 
> I've yet to see a suggestion which effectively separates 
> formatting and
> parameter ordering.  I'd like to.  I agree that they are two different
> issues completely.  But I don't see how to separate them effectively.

I don't think that it is as simple as syntax ordering vs. not.  Syntax
ordering isn't the only advantage that comes from not requiring printf
compatibility.

> I can't resist citing CAy Horstmann's home page here:
> 
>     The March of Progress
> 
>     C 
>           printf("%10.2f", x); 
>     C++ 
>           cout << setw(10) << setprecision(2) << showpoint << x; 
>     Java 
> 
>           java.text.NumberFormat formatter 
>              = java.text.NumberFormat.getNumberInstance();
>           formatter.setMinimumFractionDigits(2);
>           formatter.setMaximumFractionDigits(2);
>           String s = formatter.format(x);
>           for (int i = s.length(); i < 10; i++)
>              System.out.print(' ');
>           System.out.print(s);
> 
> Although he forgot the fixed in C++, not to mention putting the stream
> back into it's original state.
> 
> Viewed this way, maybe the printf syntax isn't so bad afterall.

Good example.  At least Java uses fully descriptive names.  With C++, you
get not only verbosity, but you are still stuck with cryptic naming.  Why is
the code setting the unicode character width to 10 bits? :-)