Re: Review request : format

From: vonosan (alnsn_at_[hidden])
Date: 2001-12-20 04:13:02

--- In boost_at_y..., Karl Nelson <kenelson_at_e...> wrote:
> How is the execption to be handled?  What good does it do to raise 
it?
> Can you provide a reasonable code where raising an exception when
> strings are being provided from an outside source will make 
> a critical difference to the coder?
> 

Exception handling is one more little agrument against traiting 
format as manipulator. Look:
  cout << "hex: "
       << hex
       << i
       << endl;
You expected that this code will not throw exception even in stress 
memory conditions. You know that operator<<'s whether set flags or 
put characters directly to the stream buffer. This can be implemented 
safely (and I beleive it is).
Next "equivalent" example:
  cout << start_format ( "%s%x" )
       << "hex: "
       << i
       << stop_format
       << endl;
is completely different story. Characters are accumulated in format 
object and then outputed to cout. It really can throw! Users of 
ostreams expected that they can safe pass to ostream most 
manipulators and build-in types and they fail here.

> > That's a good point for % rather than <<.
> > In fact,  in my opinion, it's the strongest point. the rest is mre
> > subjective.
> > While this one is essential : we should not use << because format 
is NOT
> > a manipulator.
> 
> But is a maniplator.
> 

How are you going to implement this code?
  cout << start_format ( "hex: %x" );
  cout << i;
  cout << stop_format
       << endl;

I think most of us agree that we should somehow distinguish output to 
stream and output to format. I prefered do not mix ostream and format 
at all. Samuel Krempp prefered another operator. We all care about 
clear functionality.

---------
Alexander