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From: Steve Byan (smb_at_[hidden])
Date: 2006-01-26 09:28:05

First let me mention that I greatly appreciate all the work done by
the contributors to Boost. The library has been extremely helpful to
me both as a class and template library and as a learning tool for
template meta-programming.

In the spirit of constructive criticism, I'd like to offer a few
usability observations arising from my first attempt to use
program_options. I appreciate the flexibility, extensive feature set,
and the extensibility of the library. I particularly like the
unification of command-line options with configuration files; this is
a very handy feature. However, I think the unification of program
arguments with program options is less successful. I think the
library would be better if arguments were a separate concept.

Unifying program arguments with program options has these consequences:

1) The error message produced by an excessive number of arguments is
opaque to most users. The error message produced is "Error: unknown
option foo", which I think would be better phrased as something along
the lines of "Error: too many arguments". Since program_options
doesn't distinguish options from arguments, it can't easily produce a
better diagnostic message.

2) The usage description by default describes command-line arguments
as options. E.g. the usage message is something like this:

Supported options:
   -h [ --help ] produce this help message
   --device-file arg scsi pass-thru device special file

To hide the "argument options" in the help message, program_options
supports multiple options_descriptions, but puts the responsibility
for hiding the "argument options" on the user of the library, and,
unlike normal options, does not automatically provide a description
of the argument in the help message. If arguments were instead
treated as first-class concept instead of a mutant form of an option,
the library could automatically handle these issues.

3) Somewhat related to issue #2, program_options doesn't generate a
concise usage description help-message from the grammar. For example,
it would be nice if options_desciption could provide a string like this:

Usage: scsi_tool [-h | --help] [-v | --verbose] <device-file>

Additionally, it would be nice if program_options handled more of the
validation and error reporting. Currently the user is responsible for
checking for required arguments and generating an error if they are
not supplied, and for coding the generation of a usage message when
the options and arguments don't conform to the specified grammar.

An example of an alternative design which addresses these concerns
(but which lacks many of the more sophisticated features of
program_options) is Ole Laursen's commandoptions <http://>

Steve Byan <smb_at_[hidden]>
Software Architect
Egenera, Inc.
165 Forest Street
Marlboro, MA 01752
(508) 858-3125

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