entity_cloner_builder_split.md

---

title: EntityClonerBuilder Split
pull_requests: [19649, 19977]

---

EntityClonerBuilder is now generic and has different methods depending on the generic.

To get the wanted one, EntityCloner::build got split too:

• EntityCloner::build_opt_out to get EntityClonerBuilder<OptOut>

• EntityCloner::build_opt_in to get EntityClonerBuilder<OptIn>

The first is used to clone all components possible and optionally opting out of some. The second is used to only clone components as specified by opting in for them.

// 0.16
let mut builder = EntityCloner.build(&mut world);
builder.allow_all().deny::<ComponentThatShouldNotBeCloned>();
builder.clone_entity(source_entity, target_entity);

let mut builder = EntityCloner.build(&mut world);
builder.deny_all().allow::<ComponentThatShouldBeCloned>();
builder.clone_entity(source_entity, target_entity);

// 0.17
let mut builder = EntityCloner.build_opt_out(&mut world);
builder.deny::<ComponentThatShouldNotBeCloned>();
builder.clone_entity(source_entity, target_entity);

let mut builder = EntityCloner.build_opt_in(&mut world);
builder.allow::<ComponentThatShouldBeCloned>();
builder.clone_entity(source_entity, target_entity);

Still, using EntityClonerBuilder::finish will return a non-generic EntityCloner. This change is done because the behavior of the two is too different to share the same struct and same methods and mixing them caused bugs.

The methods of the two builder types are different to 0.16 and to each other now:

Opt-Out variant

• Still offers variants of the deny methods.

• No longer offers allow methods, you need to be exact with denying components.

• Offers now the insert_mode method to configure if components are cloned if they already exist at the target.

• Required components of denied components are no longer considered. Denying A, which requires B, does not imply B alone would not be useful at the target. So if you do not want to clone B too, you need to deny it explicitly. This also means there is no without_required_components method anymore as that would be redundant.

• It is now the other way around: Denying A, which is required by C, will now also deny C. This can be bypassed with the new without_required_by_components method.

Opt-In variant

• Still offers variants of the allow methods.

• No longer offers deny methods, you need to be exact with allowing components.

• Offers now allow_if_new method variants that only clone this component if the target does not contain it. If it does, required components of it will also not be cloned, except those that are also required by one that is actually cloned.

• Still offers the without_required_components method.

Common methods

All other methods EntityClonerBuilder had in 0.16 are still available for both variants:

• with_default_clone_fn

• move_components

• clone_behavior variants

• linked_cloning

Unified id filtering

Previously EntityClonerBuilder supported filtering by 2 types of ids: ComponentId and TypeId, the functions taking in IntoIterator for them. Since now EntityClonerBuilder supports filtering by BundleId as well, the number of method variations would become a bit too unwieldy. Instead, all id filtering methods were unified into generic deny_by_ids/allow_by_ids(_if_new) methods, which allow to filter components by TypeId, ComponentId, BundleId and their IntoIterator variations.

Other affected APIs

0.16	0.17
EntityWorldMut::clone_with	EntityWorldMut::clone_with_opt_out EntityWorldMut::clone_with_opt_in
EntityWorldMut::clone_and_spawn_with	EntityWorldMut::clone_and_spawn_with_opt_out EntityWorldMut::clone_and_spawn_with_opt_in
EntityCommands::clone_with	EntityCommands::clone_with_opt_out EntityCommands::clone_with_opt_in
EntityCommands::clone_and_spawn_with	EntityCommands::clone_and_spawn_with_opt_out EntityCommands::clone_and_spawn_with_opt_in
entity_command::clone_with	entity_command::clone_with_opt_out entity_command::clone_with_opt_in