Zachary Turner wrote:
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.
Actually I was thinking about that too and yes that would be more useful. I'm generally opposed to customization by free-standing overloads because it means you can customize only once per type, rather than per instance. So I was trying to do it with the minimum possible amount of code changes. Is there a way to implement what you suggest without breaking existing code?
I think it's fairly easy to write the code so that if no validate is specified on specific option, the free-standing one is called. However, if the decision is made at runtime it means that free-standing validate will be instantiated for every time, and it's a bit tricky to avoid. In theory, the 'validate' call may return a special type that knows that validate was specified. Then, operator(), if called with plain value_semantics, may instantiate free-standing validate and associate it with the option. I did not try this, so I don't know if that will be a mess. - Volodya