[boost] Re: boost::program_options extensions

From: Vladimir Prus (ghost_at_[hidden])
Date: 2005-01-28 08:09:28

Hi Preston,

> I've been working with boost::options, and these is one gaping hole in it,
> that I have noticed.  There is no way to use a custom converter in the
> default po::typed_value class.
.......
> validate_mapped - used as:
> value<T>()->parser(validate_mapped<K,T>(first_key, first_val)
> + std::make_pair(second_key, second_val)
> + std::make_pair(third_key, third_val))
> This will then allow you to specify a value of one type, but have a
> different type stored.  This is particularly useful to allow, say:
> LogLevel = info
> and then have that actually stored as an in (say, 5) in the values.

This is cool.

> I have others to do syntax validation too, so say validate_ipaddr which
> will ensure that it is a valid IP address before storing it, and so on.
> 
> Again, I'm not sure how much notifiers would do this too.  But also
> consider the following.
> 
> A 'validator' that allows you to take an IP address as text, verify it is
> a valid IP address (hell, if someone wanted to add logic, verify it is
> within a certain range if they wanted to), and then store it as an
> in_addr_t.

This is indeed cannot be conveniently done in the current version. You can
create a subclass of 'value_semantics', say,
"ip_address_value_semantics_t", then create a function
"ip_address_value_semantics", and use it instead of "value". But passing
just the validator function is more convenient, so I intend to implement
this functionality.

> And all in all, the change to do this was minimal, apart from adding the
> 'parser' function, my xparse function is simply:
> if (m_parser)
> m_parser(value_store, new_tokens)
> else
> validate(value_store, new_tokens, (T*) 0, 0);
> 
> Feel free to e-mail me if you want my code, or want me to post it.

I understand what your change is, so I can quickly apply it myself. I'll
only need to decide if it's better to provide custom parser, custom
validator (called after parsing), or both. And I also need to find out
what's sizeof(boost::function<....>) is ;-)

Thanks,
Volodya