D++ (DPP)
C++ Discord API Bot Library
Making expiring buttons with when_any

Warning
D++ Coroutines are a very new feature and are currently only supported by D++ on g++ 11, clang/LLVM 14, and MSVC 19.37 or above. Additionally, D++ must be built with the CMake option DPP_CORO, and your program must both define the macro DPP_CORO and use C++20 or above. The feature is experimental and may have bugs or even crashes, please report any to GitHub Issues or to our Discord Server.

In the last example we've explored how to await events using coroutines, we ran into the problem of the coroutine waiting forever if the button was never clicked. Wouldn't it be nice if we could add an "or" to our algorithm, for example wait for the button to be clicked or for a timer to expire? I'm glad you asked! D++ offers when_any which allows exactly that. It is a templated class that can take any number of awaitable objects and can be co_await-ed itself, will resume when the first awaitable completes and return a result object that allows to retrieve which awaitable completed as well as its result, in a similar way as std::variant.

#include <dpp/dpp.h>
int main() {
dpp::cluster bot{"token"};
bot.on_slashcommand([](const dpp::slashcommand_t& event) -> dpp::task<void> {
if (event.command.get_command_name() == "test") {
// Make a message and add a button with its custom ID set to the command interaction's ID so we can identify it
dpp::message m{"Test"};
std::string id{event.command.id.str()};
m.add_component(
.set_label("Click me!")
.set_id(id)
)
);
co_await event.co_reply(m);
auto result = co_await dpp::when_any{ // Whichever completes first...
event.from->creator->on_button_click.when([&id](const dpp::button_click_t &b) { // Button clicked
return b.custom_id == id;
}),
event.from->creator->co_sleep(5) // Or sleep 5 seconds
};
// Note!! Due to a bug in g++11 and g++12, id must be captured as a reference above or the compiler will destroy it twice. This is fixed in g++13
if (result.index() == 0) { // Awaitable #0 completed first, that is the button click event
// Acknowledge the click and edit the original response, removing the button
const dpp::button_click_t &click_event = result.get<0>();
click_event.reply();
event.edit_original_response(dpp::message{"You clicked the button with the id " + click_event.custom_id});
} else { // Here index() is 1, the timer expired
event.edit_original_response(dpp::message{"I haven't got all day!"});
}
}
});
bot.on_ready([&bot](const dpp::ready_t& event) {
if (dpp::run_once<struct register_bot_commands>()) {
dpp::slashcommand command{"test", "Test awaiting for an event", bot.me.id};
bot.global_command_create(command);
}
});
bot.start(dpp::st_wait);
return 0;
}

Any awaitable can be used with when_any, even dpp::task, dpp::coroutine, dpp::async. When the when_any object is destroyed, any of its awaitables with a cancel() method (for example dpp::task) will have it called. With this you can easily make commands that ask for input in several steps, or maybe a timed text game, the possibilities are endless! Note that if the first awaitable completes with an exception, result.get will throw it.

Note
when_any will try to construct awaitable objects from the parameter you pass it, which it will own. In practice this means you can only pass it temporary objects (rvalues) as most of the coroutine-related objects in D++ are move-only.
dpp::button_click_t::custom_id
std::string custom_id
button custom id
Definition: dispatcher.h:733
dpp::managed::id
snowflake id
Unique ID of object set by Discord. This value contains a timestamp, worker ID, internal server ID,...
Definition: managed.h:79
dpp::interaction_create_t::co_reply
dpp::async< dpp::confirmation_callback_t > co_reply() const
Acknowledge interaction without displaying a message to the user, for use with button and select menu...
dpp::slashcommand_t
User has issued a slash command.
Definition: dispatcher.h:715
dpp::st_wait
@ st_wait
Wait forever on a condition variable. The cluster will spawn threads for each shard and start() will ...
Definition: cluster.h:101
dpp::task
A coroutine task. It starts immediately on construction and can be co_await-ed, making it perfect for...
Definition: coro/coro.h:166
dpp::component::set_id
component & set_id(const std::string &id)
Set the id of the component. For action rows, this field is ignored. Setting the id will auto-set the...
dpp::message
Represents messages sent and received on Discord.
Definition: message.h:1758
dpp::interaction_create_t::command
interaction command
command interaction
Definition: dispatcher.h:698
dpp::component::set_type
component & set_type(component_type ct)
Set the type of the component. Button components (type dpp::cot_button) should always be contained wi...
dpp::slashcommand
Represents an application command, created by your bot either globally, or on a guild.
Definition: appcommand.h:1358
dpp::when_any
Experimental class to co_await on a bunch of awaitable objects, resuming when the first one completes...
Definition: when_any.h:170
dpp::utility::cout_logger
std::function< void(const dpp::log_t &)> DPP_EXPORT cout_logger()
Get a default logger that outputs to std::cout. e.g.
Definition: dispatcher.h:228
dpp::interaction::get_command_name
std::string get_command_name() const
Get the command name for a command interaction.
dpp::interaction_create_t::reply
void reply(command_completion_event_t callback=utility::log_error()) const
Acknowledge interaction without displaying a message to the user, for use with button and select menu...
dpp::cot_button
@ cot_button
Clickable button.
Definition: message.h:86
dpp::component
Represents the component object. A component is a clickable button or drop down list within a discord...
Definition: message.h:353
dpp::component::add_component
component & add_component(const component &c)
Add a sub-component, only valid for action rows. Adding subcomponents to a component will automatical...
dpp::cluster
The cluster class represents a group of shards and a command queue for sending and receiving commands...
Definition: cluster.h:99
dpp::button_click_t
Click on button.
Definition: dispatcher.h:723
dpp::unicode_emoji::m
constexpr const char m[]
Definition: unicode_emoji.h:5119
dpp::component::set_label
component & set_label(const std::string &label)
Set the label of the component, e.g. button text. For action rows, this field is ignored....
dpp::cluster::on_log
event_router_t< log_t > on_log
Called when a log message is to be written to the log. You can attach any logging system here you wis...
Definition: cluster.h:481
dpp::ready_t
Session ready.
Definition: dispatcher.h:981
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