states.adoc

States

State management is a useful mechanism for storing data specific to different parts of the application. All states start out as inactive, but they can be activated or deactivated at any time.

struct GameState {
    int level{};
};

auto load_next_level(State<GameState> game_state) -> void
{
    if (game_state.has_value()) {
        game_state->level++;
    } else {
        game_state.emplace(GameState{ .level = 1 });
    }
}

States are like resources wrapped inside an std::optional or an event that gets activated instantly and cleared manually. Similar to resources and events, they should also be registered in advance.

ddge::app::create()
    .plug_in(ddge::plugins::States{})
    .register_state<GameState>();