Re: [Boost-users] program_options range checking?

From: Vladimir Prus (ghost_at_[hidden])
Date: 2005-08-24 08:15:34

Hi Fredrik,

> Here is what I have now:
>      
>   /*! Check for values greater than min.
>    */
>   template <typename T>
>   class value_gt {
>   public:
>     value_gt(std::string const & msg, T min) : msg_(msg), min_(min) {}
>     void operator()(T const & v) const {
>       if (v > min_) return;
.......
>   void doSetProgram(Options & options)
>   { 
>     options.add_options()
>     ("help,h", "show this message")
>     ("density",
>       pgmopt::value<double>()->notifier(
>               value_gt<double>("density", 1.0)),
.....

> I don't like repeating the type (see code above) and would rather
> like to have access to the name of the option in the function
> that does the check.
>  
> What would be a better solution?  Adding to the validators idea
> or?

I'd suggest creating a class template derived from typed_value<T>,
overriding the 'xparse' method and adding the check there, after calling
the inherited version. This will bring your example down to:

     ("density",
       pgmopt::value_gt<double>("density", "1.0")

It would be nicer to write:

     ("density",
       pgmopt::value<double>()->validator(_1 < 1.0)

(Using boost.lambda to create validator expression), but it's not supported
yet. It's something I'd like to add, though.

- Volodya