I am trying to figure out, how to implement an option for a "verbosity" level -v. The idea is that it should be repeatable and joinable, i.e. -v should set it to 1, -vvv should set it to 3.

I have found an example for repeatable and joinable options:

auto cli = joinable(
        repeatable(
            option("a")([&]{++as;}) |
            option("b")([&]{++bs;})
        )
    );

which works fine. But when I try to define my option:

auto verb = 0;
bool d = false;
auto cli = (<...>,
        joinable(repeatable(option("-v").call(increment(verb)) % verb_help))
//        joinable(repeatable(option("-v").call(increment(verb)) % verb_help, option("-d").set(d)))
        );

the parsing fails on anything different from -v. What I found that it starts working as expected when I add "dummy" option -d to the joinable and repeatable list.