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[Merged by Bors] - Add component_id function to World and Components #5066

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Addressing documentation feedback round 3
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GarettCooper committed Jun 23, 2022
commit eddc5c22c81112059804c12a94a583da06b84c4e
22 changes: 11 additions & 11 deletions crates/bevy_ecs/src/component.rs
Original file line number Diff line number Diff line change
Expand Up @@ -141,21 +141,20 @@ impl ComponentInfo {
/// A semi-opaque value which uniquely identifies the type of a [`Component`] within a
/// [`World`](crate::world::World).
///
/// Each time a new [`Component`] type is registered within a [`World`](crate::world::World)
/// using [`World::init_component`](crate::world::World::init_component) or
/// Each time a new `Component` type is registered within a `World` using
/// [`World::init_component`](crate::world::World::init_component) or
/// [`World::init_component_with_descriptor`](crate::world::World::init_component_with_descriptor),
/// 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
/// `ComponentId`s may exist in a [`World`](crate::world::World) to track components which cannot be
/// Each Rust type registered as a `Component` will have a corresponding `ComponentId`, but additional
/// `ComponentId`s 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`](crate::world::World).
/// Attempting to use a `ComponentId` from one [`World`](crate::world::World) to access the metadata
/// of a [`Component`] in a different [`World`](crate::world::World) is undefined behaviour and should
/// not be attempted.
/// 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 behaviour
/// and should not be attempted.
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#[derive(Debug, Copy, Clone, Hash, Ord, PartialOrd, Eq, PartialEq)]
pub struct ComponentId(usize);
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I think we should consider talking a bit about the relationship with TypeId here too.

Basically, for Rust types, there's a one-to-one mapping between TypeId and ComponentId. But non-Rust components can be used (well, only kind of so far), and these also get their own ComponentId.

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I've added a new section to explain the relationship. I'm not totally happy with the last sentence "Each Rust type ... or other advanced use cases" since it's pretty clunky, but after fiddling with it for a bit I couldn't come up with anything that wasn't quite a bit more verbose. Suggestions appreciated.


Expand Down Expand Up @@ -370,12 +369,13 @@ impl Components {
self.indices.get(&type_id).map(|index| ComponentId(*index))
}

/// Retrieves the [`ComponentId`] of the given [`Component`] type `T`.
/// The returned [`ComponentId`] is specific to the `Components` instance
/// Returns the [`ComponentId`] of the given [`Component`] type `T`.
///
/// The returned `ComponentId` is specific to the `Components` instance
/// it was retrieved from and should not be used with another `Components`
/// instance.
///
/// Returns [`None`] if the [`Component`] type has not
/// Returns [`None`] if the `Component` type has not
/// yet been initialized using [`Components::init_component`].
///
/// ```rust
Expand Down
17 changes: 9 additions & 8 deletions crates/bevy_ecs/src/world/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -177,19 +177,19 @@ impl World {
WorldCell::new(self)
}

/// Initializes a new [`Component`] and returns the [`ComponentId`] created for it.
/// Initializes a new [`Component`] type and returns the [`ComponentId`] created for it.
pub fn init_component<T: Component>(&mut self) -> ComponentId {
self.components.init_component::<T>(&mut self.storages)
}

/// Initializes a new Component type and returns the [`ComponentId`] created for it.
/// Initializes a new [`Component`] type and returns the [`ComponentId`] created for it.
///
/// This method differs from [`World::init_component`] in that it uses a [`ComponentDescriptor`]
/// to initialize the new component type instead of statically available type information. This
/// enables the dynamic initialization of new component definitions at runtime for advanced use cases.
///
/// While the option to initialize a component from a descriptor is useful in type-erased
/// contexts, the standard [`World::init_component`] function should always be used instead
/// contexts, the standard `World::init_component` function should always be used instead
/// when type information is available at compile time.
pub fn init_component_with_descriptor(
&mut self,
Expand All @@ -199,12 +199,13 @@ impl World {
.init_component_with_descriptor(&mut self.storages, descriptor)
}

/// Retrieves the [`ComponentId`] of the given [`Component`] type `T`. The returned
/// [`ComponentId`] is specific to the `World` instance it was retrieved from and
/// should not be used with another `World` instance.
/// Returns the [`ComponentId`] of the given [`Component`] type `T`.
///
/// Returns [`None`] if the [`Component`] type has not yet been initialized within
/// the [`World`] using [`World::init_component`].
/// The returned `ComponentId` is specific to the `World` instance
/// it was retrieved from and should not be used with another `World` instance.
///
/// Returns [`None`] if the `Component` type has not yet been initialized within
/// the `World` using [`World::init_component`].
///
/// ```rust
/// use bevy_ecs::prelude::*;
Expand Down