Slash command auto completion

Discord now supports sending auto completion lists for slash command choices. To use this feature you can use code such as the example below:

#include <dpp/dpp.h>
 
int main()
{
    dpp::cluster bot("token");
 
        bot.on_log(dpp::utility::cout_logger());
 
    bot.on_ready([&bot](const dpp::ready_t & event) {
        if (dpp::run_once<struct register_bot_commands>()) {
            /* Create a new global command once on ready event */
            bot.global_command_create(dpp::slashcommand("blep", "Send a random adorable animal photo", bot.me.id)
                .add_option(
                    /* If you set the auto complete setting on a command option, it will trigger the on_autocomplete
                     * event whenever discord needs to fill information for the choices. You cannot set any choices
                     * here if you set the auto complete value to true.
                     */
                    dpp::command_option(dpp::co_string, "animal", "The type of animal").set_auto_complete(true)
                )
            );
        }
    });
 
    /* The interaction create event is fired when someone issues your commands */
    bot.on_slashcommand([&bot](const dpp::slashcommand_t & event) {
        /* Check which command they ran */
        if (event.command.get_command_name() == "blep") {
            /* Fetch a parameter value from the command parameters */
            std::string animal = std::get<std::string>(event.get_parameter("animal"));
            /* Reply to the command. There is an overloaded version of this
            * call that accepts a dpp::message so you can send embeds.
            */
            event.reply("Blep! You chose " + animal);
        }
    });
 
    /* The on_autocomplete event is fired whenever discord needs information to fill in a command options's choices.
     * You must reply with a REST event within 500ms, so make it snappy!
     */
    bot.on_autocomplete([&bot](const dpp::autocomplete_t & event) {
        for (auto & opt : event.options) {
            /* The option which has focused set to true is the one the user is typing in */
            if (opt.focused) {
                /* In a real world usage of this function you should return values that loosely match
                 * opt.value, which contains what the user has typed so far. The opt.value is a variant
                 * and will contain the type identical to that of the slash command parameter.
                 * Here we can safely know it is string.
                 */
                std::string uservalue = std::get<std::string>(opt.value);
                bot.interaction_response_create(event.command.id, event.command.token, dpp::interaction_response(dpp::ir_autocomplete_reply)
                    .add_autocomplete_choice(dpp::command_option_choice("squids", "lots of squids"))
                    .add_autocomplete_choice(dpp::command_option_choice("cats", "a few cats"))
                    .add_autocomplete_choice(dpp::command_option_choice("dogs", "bucket of dogs"))
                    .add_autocomplete_choice(dpp::command_option_choice("elephants", "bottle of elephants"))
                );
                bot.log(dpp::ll_debug, "Autocomplete " + opt.name + " with value '" + uservalue + "' in field " + event.name);
                break;
            }
        }
    });
 
    bot.start(false);
 
    return 0;
}