Resources as Components

#[derive(Resource)] implements the Component trait

In 0.19, Resource is a subtrait of Component and #[derive(Resource)] implements both Resource as well as Component. This means it's no longer possible to doubly derive both Component and Resource. Instead, you should split them up:

// 0.18
#[derive(Component, Resource)]
struct Dual

becomes

// 0.19
#[derive(Component)]
struct DualComp;

#[derive(Resource)]
struct DualRes;

Consequently, UiDebugOverlay is split into GlobalUiDebugOverlay (resource) and UiDebugOverlay (component), and UiDebugOptions is split into GlobalUiDebugOptions (resource) and UiDebugOptions (component).

#[reflect(Resource)] Changes

In 0.19, the ReflectResource is a ZST (zero-sized type) and only functions to signify that the trait is reflected. Instead, #[reflect(Resource)] also reflects the Component trait, so use ReflectComponent instead. This is likely to show up in code that uses reflection, like BRP (Bevy Remote Protocol) and bevy_world_serialization.

Broad Queries and System Conflicts

Now that resources are components, they can be queried using 'broad' queries. These are queries that query all entities. Examples include:

• Query<()>
• Query<Entity>
• Query<EntityMut>
• Query<EntityRef>
• Query<EntityMutExcept>
• Query<EntityRefExcept>
• Query<Option<&T>>

These should rarely come up in real games, but if they do, they might conflict with resource access, i.e.

fn system(entity_query: Query<EntityMut>, some_resource: Res<MyResource>) {} // err! entity_query conflicts with some_resource

To fix this, you can narrow down the query by using either the Without<MyResource> or Without<IsResource> filter. The IsResource marker is attached to all resource entities, so it always filters them out.

The same is true for non-send data:

fn system(entity_query: Query<EntityMut>, some_non_send: NonSend<MyNonSend>) {} // err! entity_query conflicts with some_resource

This can be fixed by adding a Without<MyNonSend> filter to the query.

Renaming Non-Send Resources to Non-Send Data

Previously there were two types of resources: Send resources and !Send resources. Now that Send resources are stored as components, !Send resources have little in common with their Send counterparts. This is why non-send resources are being renamed to non-send data. The following APIs are affected:

• App::init_non_send_resource is deprecated in favor of App::init_non_send.
• App::insert_non_send_resource is deprecated in favor of App::insert_non_send.
• DeferredWorld::non_send_resource_mut is deprecated in favor of DeferredWorld::non_send_mut.
• DeferredWorld::get_non_send_resource_mut is deprecated in favor of DeferredWorld::get_non_send_mut.
• ResourceData<SEND: true> is removed, while ResourceData<SEND: false> is renamed to NonSendData.
• Resources<SEND: true> is removed and Resources<Send: false> is renamed to NonSends.
• UnsafeWorldCell::get_non_send_resource is deprecated in favor of UnsafeWorldCell::get_non_send.
• UnsafeWorldCell::get_non_send_resource_by_id is deprecated in favor of UnsafeWorldCell::get_non_send_by_id.
• UnsafeWorldCell::get_non_send_resource_mut is deprecated in favor of UnsafeWorldCell::get_non_send_mut.
• UnsafeWorldCell::get_non_send_resource_mut_by_id is deprecated in favor of UnsafeWorldCell::get_non_send_mut_by_id.
• World::init_non_send_resource is deprecated in favor of World::init_non_send.
• World::insert_non_send_resource is deprecated in favor of World::insert_non_send.
• World::remove_non_send_resource is deprecated in favor of World::remove_non_send.
• World::non_send_resource is deprecated in favor ofWorld::non_send.
• World::non_send_resource_mut is deprecated in favor of World::non_send_mut.
• World::get_non_send_resource is deprecated in favor of World::get_non_send.
• World::get_non_send_resource_mut is deprecated in favor of World::get_non_send_mut.

Component Registration

Before using components and resources they must be registered to a world. The registration process for components and resources is very similar and now that Send resources are components, we're able to simplify some of the code; removing / deprecating some methods.

• Components::register_resource_unchecked is renamed to Components::register_non_send_unchecked.
• Components::get_valid_resource_id was deprecated in favor of Components::get_valid_id.
• Components::valid_resource_id was deprecated in favor of Components::valid_component_id.
• Components::resource_id was deprecated in favor of Components::component_id.
• ComponentsRegistrator::register_resource is deprecated in favor of ComponentsRegistrator::register_component.
• ComponentsRegistrator::register_resource_with is renamed to ComponentsRegistrator::register_non_send_with.
• ComponentsRegistrator::register_resource_with_descriptor is removed in favor of ComponentsRegistrator::register_component_with_descriptor.
• ComponentsQueuedRegistrator::queue_register_resource_with_descriptor was removed in favor of ComponentsQueuedRegistrator::queue_register_component_with_descriptor.
• ComponentsQueuedRegistrator::queue_register_resource was deprecated in favor of ComponentsQueuedRegistrator::queue_register_component.
• ComponentDescriptor::new_resource was deprecated in favor of ComponentDescriptor::new
• ComponentDescriptor::new_resource was deprecated in favor of ComponentDescriptor::new
• World::register_resource_with_descriptor was renamed to World::register_non_send_with_descriptor.

Access

Resources were also removed from Access, which keeps track what data any given query / system has access to.

• Access::add_component_read and Access::add_resource_read were deprecated in favor of Access::add_read.
• Access::add_component_write and Access::add_resource_write were deprecated in favor of Access::add_write.
• Access::remove_component_read was deprecated in favor of Access::remove_read.
• Access::remove_component_write was deprecated in favor of Access::remove_write.
• Access::has_component_read and Access::has_resource_read were deprecated in favor of Access::has_read.
• Access::has_any_component_read and Access::has_any_resource_read were deprecated in favor of Access::has_any_read.
• Access::has_component_write and Access::has_resource_write were deprecated in favor of Access::has_write.
• Access::has_any_component_write and Access::has_any_resource_write were deprecated in favor of Access::has_any_write.
• Access::read_all_components was deprecated in favor of Access::read_all.
• Access::write_all_components was deprecated in favor of Access::write_all.
• Access::read_all_resources and Access::write_all_resources were removed.
• Access::has_read_all_components was deprecated in favor of Access::has_read_all.
• Access::has_write_all_components was deprecated in favor of Access::has_write_all.
• Access::has_read_all_resources and Access::has_write_all_resources were removed.
• Access::is_components_compatible was deprecated in favor of Access::is_compatible.
• Access::is_resources_compatible was removed.
• Access::is_subset_components was deprecated in favor of Access::is_subset.
• Access::is_subset_resources was removed.
• Access::resource_reads_and_writes, Access::resource_reads, Access::resource_writes were removed.
• Access::try_iter_component_access was deprecated in favor of Access::try_iter_access.
• FilteredAccess::add_component_read was deprecated in favor of FilteredAccess::add_read.
• FilteredAccess::add_component_write was deprecated in favor of FilteredAccess::add_write.
• FilteredAccess::add_resource_read and FilteredAccess::add_resource_write were removed.
• FilteredAccess::read_all_components was deprecated in favor of FilteredAccess::read_all.
• FilteredAccess::write_all_components was deprecated in favor of FilteredAccess::write_all.
• FilteredAccessSet::add_unfiltered_resource_read was deprecated in favor of FilteredAccessSet::add_resource_read.
• FilteredAccessSet::add_unfiltered_resource_write was deprecated in favor of FilteredAccessSet::add_resource_write.

Due to the split storage it used to be possible to both access an entity and a resource in a WorldQuery implementor. This is no longer valid. In order to access multiple different entities for a WorldQuery implementation, use WorldQuery::init_nested_access. See the implementation of WorldQuery for AssetChanged for an example of how this can be done correctly.

Immutable Resources

Since resources may now be immutable, the following now carry a Mutability = Mutable bound:

• ResMut
• World::resource_mut, World::get_resource_mut
• UnsafeWorldCell::get_resource_mut
• EntityWorldMut::resource_mut, EntityWorldMut::get_resource_mut
• DeferredWorld::resource_mut, DeferredWorld::get_resource_mut
• TemplateContext::resource_mut
• as well as ExtractResourcePlugin

If you are calling these in a generic context and the resource is always mutable, you need to add this bound to your type parameter:

// 0.18
fn my_generic_system<R: Resource>(mut res: ResMut<R>) {
    …
}

// 0.19
fn my_generic_system<R: Resource<Mutability = Mutable>>(mut res: ResMut<R>) {
    …
}

If the bound cannot be added, there are a couple of options:

• If the resource is only sometimes mutable OR the API should not be unsafe, use World::modify_resource and World::modify_resource_by_id. They behave exactly like their component counterparts.
• If your API can be made unsafe, use the UnsafeWorldCell::*_assume_mutable methods and make sure that the safety conditions are satisfied. UnsafeWorldCell::get_resource_mut_assume_mutable has been provided for this explicit purpose. It is also possible to use the *_assume_mutable component methods, but you will first have to retrieve the resource entity from ResourceEntities.

Miscellaneous

Since MapEntities is implemented by default for components, it's no longer necessary to add derive(MapEntities) to a resource.

// 0.18
#[derive(Resource, MapEntities)]
struct EntityStruct(#[entities] Entity);

// 0.19
#[derive(Resource)]
struct EntityStruct(#[entities] Entity);

Next, World::clear_entities now also clears all resources, and World::clear_all now clears all entities, resources, and non-send data.

Lastly, World::remove_resource_by_id now returns bool instead of Option<()>.