Re: [boost] program_options and optional

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-06-11 07:35:30

Hi Neal,

> Seems natural to use boost::optional with program_options.  Has anyone
> tried this?

This request is amount my "todo" list since formal review, but I still haven't 
implemented it. The biggest problem is to make it work without adding 
dependency on <boost/optional.hpp> 

>     ("help", "produce help message")
>     ("x", po::value<double>()->notifier (var(x)=_1))
>     ;
>
> To set the optional<double> x, this uses boost::lambda.  Is there a more
> direct approach?

One thing I consider is to forward-declare boost::optional and then add a 
templated constructor to 'typed_value' which will do the same thing that 

    notifier (var(x)=_1)

does above. Another possibility is to make the type of pointer stored in 
'typed_value' into a template parameter. But that would not help, since 
optional can be read like pointer, but can't be assigned with *opt = 10;

I'll try to think more about the first approach, but it might take some time, 
since now I'm primarily focused an fixing regression test failures.

- Volodya