r/cpp

I've been very excited about reflection so I built a small library to pass command line arguments

Basic example:

struct Args
{
    std::string first_name;
    int age;
    bool active;
};

// ./program --first-name John --age 99 --active

const auto args = clap::parse<Args>(argc, argv);

assert(args.first_name == "John");
assert(args.age == 99);
assert(args.active);

More interesting example:

struct Args
{
    [[= clap::Description<"host to connect to">{}]]
    std::string host = "localhost";

    [[=clap::ShortName<'p'>{}]]
    std::uint16_t port;

    [[=clap::Env<"RETRY_COUNT">{}]]
    std::uint32_t retry_count;

    std::optional<std::string> log_file;

    [[=clap::ShortName<'e'>{}]]
    bool encrypted;

    [[=clap::ShortName<'c'>{}]]
    bool compressed;

    [[=clap::ShortName<'h'>{}]]
    bool hashed;
};

// ./program -p 8080 -ec

const auto args = clap::parse<Args>(argc, argv);

assert(args.host == "localhost");
assert(args.port == 8080);
assert(args.retry_count == std::stoul(std::getenv("RETRY_COUNT")));
assert(!args.log_file);
assert(args.encrypted);
assert(args.compressed);
assert(!args.hashed);

The amount of code to handle this is actually quite minimal < 500 lines.

There's a few modern goodies that make this code work:

• Reflection []

• Contracts []

• Annotations for Reflection []

• constexpr exceptions []

I guess we don't know what "idiomatic" reflection usage is like yet, I'm interested to come back to this code in a years time and see what mistakes I made!

Link to the code:

Any feedback, queries, questions are welcome!