Group of single parameter

[Jerry-Ma]

Hi,

I am playing around this lib right now and found it is great.

I wanted to created a group of one prarameter:

cli = (
    "group 1" % (
        option("-a").set(a) % "option a"
    ),
    "group 2" % (
        option("-b").set(b) % "option b",
        option("-c").set(c) % "option c"
    )
)

but the documentation generated from this is incorrect:

-a    group1
group2
    -b option b
    -c option c

The problem is that when there is only one entry in the parenthesis, no group is created. I tried doing clipp::group(option("-a").set(a) % "option a") but it seems does not fix the problem.

Any idea?

[muellan]

I see the problem. Unfortunately, the expressions ( object ) and object are equivalent and C++ doesn't offer any way to distinguish between them.

But the following works for me:

auto cli = (
        "group 1" % group(
            option("-a").set(a) % "option a"
        ),
        "group 2" % (
            option("-b").set(b) % "option b",
            option("-c").set(c) % "option c"
        )
    );

which results in the following documentation:

       group 1
            -a      option a

        group 2
            -b      option b
            -c      option c

There is another "hacky" solution:

auto cli = (
        "group 1" % (
            option("-a").set(a) % "option a",
            option("")       // <-- empty option forces group
        ),
        "group 2" % (
            option("-b").set(b) % "option b",
            option("-c").set(c) % "option c"
        )
    );

[Jerry-Ma]

@muellan

But the following works for me:

"group doc" % group(option(...) % "opt doc") for some reason does not work for me. After looking at the source code, I found the following work around: "group doc" % group("", option(...) % "opt doc").

[muellan]

Hm, that's odd. What compiler do you use?

[Jerry-Ma]

It turns out that my initial example was not the one that has the problem. Below is the correct MWE:

// main.cpp
#include <iostream>
#include "include/clipp.h"

int main([[maybe_unused]] int argc, [[maybe_unused]] char* argv[]) { 

    using namespace clipp; using std::cout; using std::string;
    bool a, b, c;
    auto cli = (
            "group 1" % group(
                "",  // this is needed to avoid calling the copy c'tor
                (option("-a").set(a) & value("A"))  % "option a"
            ),
            "group 2" % (
                option("-b").set(b) % "option b",
                option("-c").set(c) % "option c"
            )
        );
    cout << make_man_page(cli, argv[0]);
}

run with clang main.cpp -std=c++17 -lc++ && ./a.out

As pointed out in the inline comment, the outer group(...) will resolve to the copy constructor if the inner item is an option(...) & value(...) pair (i.e., a group). The empty docstring "" has to be used to make sure a new group is created.

[muellan]

Ah - that makes sense. Right now I can't think of a way to resolve this other than using the hack with an additional empty option or empty string.