Support for enumerations

[Maktm]

I tried the following code to see whether CLI11 supports the use of enumerations in add_set and got a series of errors. Is the code wrong is support for enumerations planned/not going to be added?

#include <iostream>
#include <string>

#include <CLI/CLI.hpp>

enum Level : std::int32_t
{
  High,
  Medium,
  Low
};

int main(int argc, char* argv[])
{
  CLI::App app{"App description"};
  try
  {
    Level level;
    app.add_set("-l,--level", level, {Level::High, Level::Medium, Level::Low}, "Level settings");
    app.parse(argc, argv);
  }
  catch (CLI::Error const& e)
  {
    app.exit(e);
  }
  return EXIT_SUCCESS;
}

Errors:

1>f:\github\cli11\include\cli\typetools.hpp(108): error C2440: '=': cannot convert from 'std::string' to 'Level'
1>f:\github\cli11\include\cli\typetools.hpp(108): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>f:\github\cli11\include\cli\app.hpp(326): note: see reference to function template instantiation 'bool CLI::detail::lexical_cast<T,0>(std::string,T &)' being compiled
1>        with
1>        [
1>            T=Level
1>        ]
1>f:\code\visual studio 2017\projects\cmdapp\cmdapp\main.cpp(20): note: see reference to function template instantiation 'CLI::Option *CLI::App::add_set<Level>(std::string,T &,std::set<Level,std::less<_Kty>,std::allocator<_Kty>>,std::string,bool)' being compiled
1>        with
1>        [
1>            T=Level,
1>            _Kty=Level
1>        ]
1>Done building project "cmdapp.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

[henryiii]

I'm curious, what do you expect for the interface? -l 0 or -l High? The second can't work since C++ does not have reflection, so it can't know that High == "0". The first one should have worked, though.

I'll have to see why the SFINAE is selecting the string version for a enum that just wraps an int, though, that should not be happening.

std::is_enum needs to be added along with std::is_int. Would have thought is_int would include enums.

[henryiii]

By the way, there is no need to wrap the first couple of lines with try, unless you catch CLI::Error instead of CLI::ParseError. The CLI::ConstructionErrors are not ParseErrors. (Catching CLI::Error instead is perfectly valid) (fixed in example)

[Maktm]

I'm curious, what do you expect for the interface? -l 0 or -l High?

The first version (i.e. -l 0) and it would be useful if the help message outputted something like this:

Options: -l,--level enum/Level in {High=0, Medium=1, Low=2} Level Settings

[henryiii]

C++ can't capture the names of enumerations. See this question. You can manually set that in your help string, though.

[henryiii]

Current implementation:

 Level level;
 app.add_set("-l,--level", level, {High, Medium, Low}, "Level settings")
     ->set_type_name("enum/Level in {High=0, Medium=1, Low=2}");

henrys-mbp:build henryiii$ ./examples/enum -h
Usage: ./examples/enum [OPTIONS]
Options:
  -h,--help                   Print this help message and exit
  -l,--level enum/Level in {High=0, Medium=1, Low=2}
                              Level settings

May think about this a little more. Still need to add a few tests.

[lambdafu]

This issue is closed, but I think it would be nice if we could support enums with string identifiers instead integers. I am currently using add_set together with stream operators, but that is false sharing (the stream operators may have a different purpose elsewhere), and more work than it should be (with a weird way to report conversion error). Maybe a map could be used instead?

namespace rang {
std::istream& operator>>(std::istream& in, rang::control& when) {
  std::string label;
  in >> label;
  if (label == "always")
    when = rang::control::Force;
  else if (label == "never")
    when = rang::control::Off;
  else if (label == "auto")
    when = rang::control::Auto;
  else {
    // We are not pushing back what we couldn't parse.  Seems to be OK.
    in.setstate(std::ios_base::failbit);
  }
  return in;
}

std::ostream& operator<<(std::ostream& in, const rang::control& when) {
  switch (when) {
    case rang::control::Force:
      return in << "always";
    case rang::control::Off:
      return in << "never";
    default:
      return in << "auto";
  }
}
}  // namespace rang

class GlobalOptions {
 public:
  rang::control color{rang::control::Auto};
} options;

CLI::App app;
app.add_set("--color", options.color,
            {rang::control::Auto, rang::control::Force, rang::control::Off},
            "colorize the output (auto, always, or never)")
    ->set_type_name("WHEN");

app.set_callback([&options]() { rang::setControlMode(options.color); });

[henryiii]

I'd prefer (I think) a custom class in CLI11 that would support this. Something like CLI::Set with CLI::SetOption items. Maybe could even roll in case insensitivity too.

[lambdafu]

I also tried overloading literal_cast, but it wasn't effective, probably because I didn't define it early enough or so.

[henryiii]

Okay, with IsMember mapping and built-in support for enums, I think this is finally part of CLI11, headed for 1.8!