[boost] Re: program_options bool_switch usage string ... how to prettify?

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-09-15 04:53:38

Hi Jonathan,

>> Now this is better:
>>
>>>bool help_flag;
>>>options.add_options()
>>>        ("help,h", bool_switch(&help_flag),"produce help message");
>>>
>>>  
>>>
>>
>> I tried it, and it works, but the usage string is a little odd:
>>
>>   -h [ --help ] arg (=0)    : produce help message
>>   -v [ --version ] arg (=0) : print the version number
> 
> 
> Apologies for self-reply:
> 
> It turns out that the "optional" nature of the argument to a bool_switch
> creates an impossible situation when positional arguments are used.  For
> instance:
> 
> myprogram -h positional_argument
> 
> will try to parse positional_argument as a bool if I use a bool_switch
> for the -h option
> 
> This seems like fairly useless behavior; bool_switch should *never*
> expect any argument (or, I should say, I'd like a version that doesn't
> consume my positional parameters).

I've changed bool_switch so that it does not accept any arguments. This also
solves the problem with "arg (=0)" output.

There's one possible problem. For command line, we most likely don't want
explicit value for bools. But in config file, the value is always present.
This is the only case I know where single options description for command
line and other sources is problematic -- if you describe an option with
bool_switch, it can't be specified in config file.

Let's see if that's a problem.

> Also, in parsers.cpp,
> 
> throw too_many_positional_options_error(
>                             "too much positional options");
> 
> should be "too many positional options".

Thanks, fixed.

> Similarly, is there some easy to use hook for customizing the "arg" to
> indicate the type of the data (similar to how the textual representation
> of the default argument can be changed, e.g.
> value<Infile>(&forests_file)->default_value(default_in,"STDIN"), so that
> I could get something like: "-f filename (=STDIN)   :" instead of "-f
> arg (=STDIN)  :"?

No, it's not possible at the moment. Since its not a showstopper, I'd like
to take some time to think about it. The typed_value class is getting too
big...

- Volodya