From: Vladimir Prus (ghost_at_[hidden])
Date: 2003-05-26 01:41:08
Pavol Droba wrote:
>> The only problem with current 'validator' is that it should validate
>> *string* and return the value. So, the example given by Tanton:
>> _1 >= 1 && _1 <= 9)
>> would not really work --- the validator function is given a string. It's
>> probably possible to use 'notify' callback to do such kind of validation,
>> though. Or add another validator --- which is given converted value.
> I see. However I think this is a little bit clumsy to use. I think it may
> be better to strip validation from the conversion.
> What I had in mind is an extension to po::parameter funtion to something
> template< typename T >
> *unspecified* po::parameter<T>(
> string parameter_name,
> T& variable,
> const boost::function1<bool, T)& validator );
> so the framework would convert string parameter to a specified type and
> then run the validator functor on the result to validate it.
I was actually thinking about splitting current "validator" into
"interpreter", which converts string to value and validator proper. That
should allow to write
("compression", parameter<int>("n"), "compression quality").
validator(1 < _1 && _1 <= 9)
With this feature in place, adding validator as additional argument to
'parameter' can be considered a convenience. (Now, there are 3 ideas for
additional arguments to 'parameter', so I can't decide right now).
One problem: the above would require implementation tricks. The value
extracted from string is stored in boost::any. Sure, you can't pass
boost::any to the lambda function above, so some means to recover the type
stored in any would be needed. I'm not yet sure this will be all that big
>> > I mean something like "%02.4f" or something like that... it is just an
>> > idea. If there would be a validation predicate as an argument, regex
>> > library can be used to define regex predicate which would cover most of
>> > the cases.
>> Ah... ok. Indeed --- the validator can do that already, and in case of
>> string validation, the current code will work.
> That's nice. Can you post a piece of code as an example?
Attached is a complete example which uses regex library to validate option's
value. The format of value is fictional, but the main idea should be clear.
And there's example session:
bash-2.05b$ bin/gcc/debug/regex --help
Usage: regex [options]
--help : produce a help screen
-v [ --version ] : print the version number
-m [ --magic ] arg : magic value (in NNN-NNN format)
bash-2.05b$ bin/gcc/debug/regex -m 123
bash-2.05b$ bin/gcc/debug/regex -m 123-345
The magic is "345"
I've also realized there are no examples for custom validator now, so this
code will most likely be added to the library.
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