Struct bevy::ecs::component::ComponentId

pub struct ComponentId(/* private fields */);

Expand description

A value which uniquely identifies the type of a Component of Resource within a World.

Each time a new Component type is registered within a World using e.g. World::init_component or World::init_component_with_descriptor or a Resource with e.g. World::init_resource, a corresponding ComponentId is created to track it.

While the distinction between ComponentId and TypeId may seem superficial, breaking them into two separate but related concepts allows components to exist outside of Rust’s type system. Each Rust type registered as a Component will have a corresponding ComponentId, but additional ComponentIds may exist in a World to track components which cannot be represented as Rust types for scripting or other advanced use-cases.

A ComponentId is tightly coupled to its parent World. Attempting to use a ComponentId from one World to access the metadata of a Component in a different World is undefined behavior and must not be attempted.

Given a type T which implements Component, the ComponentId for T can be retrieved from a World using World::component_id() or via Components::component_id(). Access to the ComponentId for a Resource is available via Components::resource_id().

Implementations§

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impl ComponentId

pub const fn new(index: usize) -> ComponentId

Creates a new ComponentId.

The index is a unique value associated with each type of component in a given world. Usually, this value is taken from a counter incremented for each type of component registered with the world.

pub fn index(self) -> usize

Returns the index of the current component.

Examples found in repository ?

examples/ecs/dynamic.rs (line 101)

fn main() {
    let mut world = World::new();
    let mut lines = std::io::stdin().lines();
    let mut component_names = HashMap::<String, ComponentId>::new();
    let mut component_info = HashMap::<ComponentId, ComponentInfo>::new();

    println!("{}", PROMPT);
    loop {
        print!("\n> ");
        let _ = std::io::stdout().flush();
        let Some(Ok(line)) = lines.next() else {
            return;
        };

        if line.is_empty() {
            return;
        };

        let Some((first, rest)) = line.trim().split_once(|c: char| c.is_whitespace()) else {
            match &line.chars().next() {
                Some('c') => println!("{}", COMPONENT_PROMPT),
                Some('s') => println!("{}", ENTITY_PROMPT),
                Some('q') => println!("{}", QUERY_PROMPT),
                _ => println!("{}", PROMPT),
            }
            continue;
        };

        match &first[0..1] {
            "c" => {
                rest.split(',').for_each(|component| {
                    let mut component = component.split_whitespace();
                    let Some(name) = component.next() else {
                        return;
                    };
                    let size = match component.next().map(|s| s.parse::<usize>()) {
                        Some(Ok(size)) => size,
                        _ => 0,
                    };
                    // Register our new component to the world with a layout specified by it's size
                    // SAFETY: [u64] is Send + Sync
                    let id = world.init_component_with_descriptor(unsafe {
                        ComponentDescriptor::new_with_layout(
                            name.to_string(),
                            StorageType::Table,
                            Layout::array::<u64>(size).unwrap(),
                            None,
                        )
                    });
                    let Some(info) = world.components().get_info(id) else {
                        return;
                    };
                    component_names.insert(name.to_string(), id);
                    component_info.insert(id, info.clone());
                    println!("Component {} created with id: {:?}", name, id.index());
                });
            }
            "s" => {
                let mut to_insert_ids = Vec::new();
                let mut to_insert_data = Vec::new();
                rest.split(',').for_each(|component| {
                    let mut component = component.split_whitespace();
                    let Some(name) = component.next() else {
                        return;
                    };

                    // Get the id for the component with the given name
                    let Some(&id) = component_names.get(name) else {
                        println!("Component {} does not exist", name);
                        return;
                    };

                    // Calculate the length for the array based on the layout created for this component id
                    let info = world.components().get_info(id).unwrap();
                    let len = info.layout().size() / std::mem::size_of::<u64>();
                    let mut values: Vec<u64> = component
                        .take(len)
                        .filter_map(|value| value.parse::<u64>().ok())
                        .collect();
                    values.resize(len, 0);

                    // Collect the id and array to be inserted onto our entity
                    to_insert_ids.push(id);
                    to_insert_data.push(values);
                });

                let mut entity = world.spawn_empty();

                // Construct an `OwningPtr` for each component in `to_insert_data`
                let to_insert_ptr = to_owning_ptrs(&mut to_insert_data);

                // SAFETY:
                // - Component ids have been taken from the same world
                // - Each array is created to the layout specified in the world
                unsafe {
                    entity.insert_by_ids(&to_insert_ids, to_insert_ptr.into_iter());
                }

                println!("Entity spawned with id: {:?}", entity.id());
            }
            "q" => {
                let mut builder = QueryBuilder::<FilteredEntityMut>::new(&mut world);
                parse_query(rest, &mut builder, &component_names);
                let mut query = builder.build();

                query.iter_mut(&mut world).for_each(|filtered_entity| {
                    let terms = filtered_entity
                        .components()
                        .map(|id| {
                            let ptr = filtered_entity.get_by_id(id).unwrap();
                            let info = component_info.get(&id).unwrap();
                            let len = info.layout().size() / std::mem::size_of::<u64>();

                            // SAFETY:
                            // - All components are created with layout [u64]
                            // - len is calculated from the component descriptor
                            let data = unsafe {
                                std::slice::from_raw_parts_mut(
                                    ptr.assert_unique().as_ptr().cast::<u64>(),
                                    len,
                                )
                            };

                            // If we have write access, increment each value once
                            if filtered_entity.access().has_write(id) {
                                data.iter_mut().for_each(|data| {
                                    *data += 1;
                                });
                            }

                            format!("{}: {:?}", info.name(), data[0..len].to_vec())
                        })
                        .collect::<Vec<_>>()
                        .join(", ");

                    println!("{:?}: {}", filtered_entity.id(), terms);
                });
            }
            _ => continue,
        }
    }
}