| D++ (DPP) C++ Discord API Bot Library

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Making expiring buttons with when_any

Warning
  D++ Coroutines are currently only supported by D++ on g++ 13, clang/LLVM 14, and MSVC 19.37 or above. Additionally, your program has to support C++20.

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_log(dpp::utility::cout_logger());
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(
dpp::component{}.add_component(
dpp::component{}
.set_type(dpp::cot_button)
.set_label("Click me!")
.set_id(id)
)
);
co_await event.co_reply(m);
auto result = co_await dpp::when_any{ // Whichever completes first...
event.owner->on_button_click.when([&id](const dpp::button_click_t& b) { // Button clicked
return b.custom_id == id;
}),
event.owner->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;
}
dpp::cluster
The cluster class represents a group of shards and a command queue for sending and receiving commands...
Definition cluster.h:89
dpp::cluster::global_command_create
void global_command_create(const slashcommand &s, command_completion_event_t callback=utility::log_error())
Create a global slash command (a bot can have a maximum of 100 of these).
dpp::cluster::start
void start(start_type return_after=st_wait)
Start the cluster, connecting all its shards.
dpp::cluster::on_slashcommand
event_router_t< slashcommand_t > on_slashcommand
Called when a slash command is issued. Only dpp::ctxm_chat_input types of interaction are routed to t...
Definition cluster.h:747
dpp::cluster::on_ready
event_router_t< ready_t > on_ready
Called when a shard is connected and ready. A set of cluster::on_guild_create events will follow this...
Definition cluster.h:855
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:705
dpp::cluster::co_sleep
async< timer > co_sleep(uint64_t seconds)
Get an awaitable to wait a certain amount of seconds. Use the co_await keyword on its return value to...
dpp::cluster::me
dpp::user me
The details of the bot user. This is assumed to be identical across all shards in the cluster....
Definition cluster.h:255
dpp::component
Represents the component object. A component is a clickable button or drop down list within a discord...
Definition message.h:497
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::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::interaction::get_command_name
std::string get_command_name() const
Get the command name for a command interaction.
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:39
dpp::slashcommand
Represents an application command, created by your bot either globally, or on a guild.
Definition appcommand.h:1449
dpp::task
A coroutine task. It starts immediately on construction and can be co_await-ed, making it perfect for...
Definition task.h:95
dpp::when_any
Experimental class to co_await on a bunch of awaitable objects, resuming when the first one completes...
Definition when_any.h:151
dpp::unicode_emoji::b
constexpr const char b[]
Definition unicode_emoji.h:5255
dpp::unicode_emoji::id
constexpr const char id[]
Definition unicode_emoji.h:5229
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.
dpp::run_once
auto run_once()
Run some code within an if() statement only once.
Definition once.h:41
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:72
dpp::cot_button
@ cot_button
Clickable button.
Definition message.h:48
dpp::button_click_t
Click on button.
Definition dispatcher.h:814
dpp::button_click_t::custom_id
std::string custom_id
button custom id
Definition dispatcher.h:824
dpp::event_dispatch_t::owner
dpp::cluster * owner
Cluster owning the event dispatch.
Definition dispatcher.h:102
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::interaction_create_t::command
interaction command
command interaction
Definition dispatcher.h:789
dpp::message
Represents messages sent and received on Discord.
Definition message.h:2363
dpp::ready_t
Session ready.
Definition dispatcher.h:1072
dpp::slashcommand_t
User has issued a slash command.
Definition dispatcher.h:806

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.

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