Re: [boost] Preliminary submission: command line & config file li brary

From: Rob Stewart (stewart_at_[hidden])
Date: 2003-02-18 13:15:37

From: Vladimir Prus <ghost_at_[hidden]>
> Rob Stewart wrote:
> 
> > The purpose of command line parsing is to decode the arguments
> > list into pieces of information, abstracting the syntax of the
> > command line away from the program.  Thus, the library should be
> > able to understand any of various encoding schemes.
> 
> That's syntantic level. I believe it should be as independent from
> meaning of options as possible: command line, preferrable, should
> be immediately parsable by humans.

I think we're saying the same thing.  My point is that the
library should abstract the parsing such that the program need
only describe the supported options and query to learn which have
been set and with what values.  The format those parameters take
on the command line or in a configuration file should be hidden.

> > The question then becomes how the library should provide the
> > values from the command line.  There are a number of fundamental
> > types that could be exposed by the library: bool, long, double,
> > and string.  The question is whether the library should support
> > any others.  I selected those types because Boolean and string
> > parameters are obviously important, and long and double would
> > handle pretty much all numeric arguments one would put in a
> > command line.
> 
> The level 2 of my library provides only syntantic representation
> of the read options. See
> 
>      http://zigzag.cs.msu.su:7813/program_options/html/
> 
> for the list of layers.

I can't access that page, but I was simply suggesting that the
library can expose a rather minimal set of types gleaned from the
command line.  Client code can transform from those types to
anything else desired.  Boolean and string parameters are
obvious.  Nothing else is needed as strings can (obviously)
represent all other arguments.

> > Sure, you could provide a means to read a file line by line and
> > pass each line to a parser of some sort.  However, given all of
> > the ways to parse the text one might find in such a file, I don't
> > see how that could be done so it is sufficiently flexible and yet
> > actually provides value.  IOW, the parsing would be little more
> > than read a line, give it to the parser, read another line, give
> > it to the parser, etc.  That certainly doesn't justify a special
> > library.
> 
> What "special library"?

I see two libraries in what you've proposed: one that manages
command line parsing and one that manages configuration file
parsing.  If command line and configuration file parsing are
completely abstracted from the parameter
specification/management, then it's a question of what
configuration formats are provided by default, possibly bloating
client code unnecessarily.

> > Perhaps I've missed some valuable service that should be included
> > in the proposed library, but I can't see that it should do more
> > than what I've outlined herein.  If you do, please enlighten me!
> 
> It looks like you don't need some of the extra features that both Gennadiy
> and myself are after. For example, custom value interpreration or automatic
> help message?

An automatic help message is certainly useful; I simply didn't
mention it specifically.  Custom value interpretation strikes me
as overkill.  If your library provides a string corresponding to
a particular parameter, I can use that string in myriad ways to
produce information for my program.  Putting that logic into a
command line parsing library seems over the top.

> Could you please tell which features in both designs are unnecessary and 
> should be removed?

I don't know the full set of features either of you have provided
at the moment, but I hope the above clarifies my thoughts on the
scope of such a library.

I'll second the question raised regarding the more complex
parsing: isn't that the job of a tool like Spirit?  Be careful to
avoid doing too much in this library.  You can make it really
powerful and capable, but that alone may keep too many at bay.

-- 
Rob Stewart                           stewart_at_[hidden]
Software Engineer                     http://www.sig.com
Susquehanna International Group, LLP  using std::disclaimer;