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Subject: Re: [boost] program_options custom validators
From: Vladimir Prus (vladimir_at_[hidden])
Date: 2009-07-11 03:21:04

Zachary Turner wrote:

> Hello, recently I was faced with a situation of writing a custom
> validator for a certain command line option I wanted to handle. The
> validator was supposed to check whether the value on the command line
> was in a certain range. After some head scratching, I realized
> there's no elegant way to do this with the current validation overload
> function. In the end I just ended up doing the validation after the
> options had been parsed.
> I was thinking about a good way to support this, and I thought that
> maybe the best way is to add an additional value semantic so that the
> validate function could instead be:
> template<class T, class validation_data>
> void validate(boost::any& v, const std::vector<std::string>& values,
> const validation_data& data, T* target_type, int);
> and we could write
> add_options() ("test", value<int>()->validate(boost::interval<int>(1, 10)) );
> this would require the user to provide the following overload:
> void validate(boost::any& v, std::vector<std::string>& values, const
> boost::interval<int>& data, int* target_type, int);

Would it be a more generally useful approach to add value_semantics::validate that
can take any function, and call that, in preference to the free-standing validate?
Then, you'd implement is_in_range helper and use it like

        add_options() ("test", value<int>()->validate(is_in_range(1, 10)) );


That is something I wanted to do for a while, but never found the time.

- Volodya

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