Boost C++ Libraries: Ticket #7495: Support for boost::optional in boost::program_options

anonymous — Wed, 06 Aug 2014 10:58:40 GMT

I am very interested in this as well!

anonymous — Fri, 02 Oct 2015 07:36:47 GMT

fakong@… — Mon, 19 Oct 2015 02:44:27 GMT

you only need to include this piece of code

template<class T> std::istream& operator>>(std::istream& in, boost::optional<T>& obj) {

T value; in >> value; obj = value; return in;

}

Vladimir Prus — Mon, 19 Oct 2015 05:31:14 GMT

It would seem such streaming support should be done in the optional library, not in program_options?

Fri, 30 Oct 2015 10:44:57 GMT

Implementing optional support via streaming would have unwanted side effects. The correct place to implement optional support is via the validate customization point:

namespace boost {
template<class T>
void validate(boost::any& v, std::vector<std::string> const& values, boost::optional<T>* typeTag, int)
{
    if (!values.empty())
    {
        boost::any a;
        using namespace boost::program_options;
        validate(a, values, (T*)0, 0);
        v = boost::any(boost::optional<T>(boost::any_cast<T>(a)));
    }
}
}

Vladimir Prus — Fri, 30 Oct 2015 10:48:29 GMT

Pull request will be welcome. Is there a way to implement this with a forward declaration, so that program_options do not have to depend on boost::optional.

Tue, 03 Nov 2015 19:23:58 GMT

Submitted pull request: https://github.com/boostorg/program_options/pull/18

Uses forward declaration to avoid dependency (except in tests).

status changed; resolution set

Vladimir Prus — Wed, 21 Dec 2016 10:47:41 GMT

status new → closed
resolution → fixed