Re: [boost] Boost.Format syntax

From: James Kanze (kanze_at_[hidden])
Date: 2002-02-09 09:37:07

"Brey, Edward D" <EdwardDBrey_at_[hidden]> writes:

|>  > From: Darin Adler [mailto:darin_at_[hidden]]

|>  > > I've been putting some thought into the syntax of Boost.Format,
|>  > > and have come to see that the best syntax going forward is one
|>  > > that does not try to retain compatibility with printf as a high
|>  > > priority.

|>  > I don't agree with this premise.

|>  Even though that statement was at the top of my email, it isn't
|>  really a premise.  It's really a conclusion.  Printf compatibility
|>  and elegant syntax are mutually exclusive, in light of what can be
|>  done with more modern syntaxes.  Therefore, ... (the above).

|>  > While I think it might be useful to pursue a 
|>  > string-formatting library that
|>  > doesn't have printf compatibility, I do think that a library 
|>  > that provides
|>  > printf compatibility is quite useful, and is nearly 
|>  > accomplished with the
|>  > proposed format library. That is the reason I propose 
|>  > removing the "%1" from
|>  > the library and retaining only the "%1$s" form. I don't think that the
|>  > precedence problem with operator % is severe.

|>  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.  Normally, this would be something along the lines of:

    format( gettext( "%1$s %2$s" ) )
        .with( count )
        .with( gettext( fruitNames[ count == 1 ] ) )

|>  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.

|>  > For what it's worth, where printf compatibility is not an issue in
|>  > my programs, I use a formatting system with a syntax like this:

|>  >     "There's no space left on the disk named <disk>."

|>  You're in luck.  C++ has this!
|>  cout << "There's no space left on the disk named " << disk << ".";

|>  <big grin>
|>  Of course, I agree with you.  Something like this could be quite
|>  nice to have.

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.

-- 
James Kanze                                mailto:kanze_at_[hidden]
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