RE: [boost] Thoughts on Format

From: Stewart, Robert (stewart_at_[hidden])
Date: 2002-01-24 08:39:10

From:	Karl Nelson [SMTP:kenelson_at_[hidden]]
> 
> > > Try deviating from the printf-like notation in the format string since
this
> > > isn't allowing for any printf-like functionality:
> > > 
> > > format("[3], [1] [2]-th try")[40.23](hex)[50]["toto"];
> 
> This format statement is rediculously overblown.  I have enough problems
> with overloading the modulus operator to something non-directional.
> making [] take non-integer arguments seems totally out of place.  

Are you familiar with std::map?  It offers the subscript operator as a way
of accessing elements, and the keys need not be integers.  Consequently,
there is precedence for non-integer arguments between "[" and "]".

> Can we stick to just the format with operator <<, format with operator
> %, and format with variable arguments for the discussion?

No, but we can discuss that, too.

> I still think that it is not unrealistic to simply write
> 
>   format(cout,"%3$s, %1$s %2$s-th try") << 40.23 << hex << 50 << "toto" ;
> 
> It looks like a stream and it is compact. 

I'm not the least bit familiar with Unix98 printf() format specifiers, so I
don't know what that format means.  (I purposely skipped that part of the
documentation, because printf() compatibility is not important to me.)  I'm
going to guess that the printf() % specifiers can have an embedded
positional indicator which is a number followed by $.  Given that, and
assuming that format complains at compile time when %s isn't given a string
as shown in your example, I still have one problem: I can't tell whether
"hex" is a variable in scope at this point, or whether it std::hex brought
into scope via some IOStreams header.  That may not be a likely point of
confusion for "hex," but my point is that you can't tell that 50 is argument
2, not 3.

> > By the way, Robert's approach doesn't mention about how to write
brackets.
> > Maybe we can have "%[" be a literal open square bracket, "%]" be a
literal
> > close square bracket, and "%%" be a literal percent.
> 
> Why must we confuse the user with dozens of new concepts like the above?
> Printf format is well defined and widely used.  Besides in an mixed
> code you would not want to send format strings with mixed formats.
> This point has been discussed many times over.  If we are going to 
> have a "formatted printing" it should be "formatted".  If you
> want to resubmit a "reorder" manipulator for C++ streams it 
> may be appropraite, but it does not negate the need for a 
> formatted printing operator.

Indeed, the point I made was to split the two.

Rob
Susquehanna International Group, LLP
http://www.sig.com