Struct Entities 

pub struct Entities { /* private fields */ }

Hands out entity slots and recycles them.

Implementations

impl Entities

pub fn new() -> Self

An allocator with no slots yet.

pub fn len(&self) -> usize

How many entities are alive.

pub fn is_empty(&self) -> bool

Whether no entity is alive.

pub fn capacity(&self) -> usize

The highest slot ever allocated, which bounds an ordered walk.

pub fn spawn(&mut self) -> Entity

Allocate an entity, reusing a free slot when one exists.

Reuse is newest-first, which keeps the index range compact: an ordered query walks slots rather than entities, so a store whose indices are spread thin pays for the gaps.

Panics

Never in practice: the slot count is bounded by u32::MAX, and a tree with four billion live entities has other problems. Written as a saturating count rather than an unwrap so there is no panic to reason about.

pub fn is_alive(&self, entity: Entity) -> bool

Whether this exact handle still names a live entity.

Both halves are checked. A handle whose slot is alive but whose generation is stale names an entity that no longer exists, and is the whole reason the generation is there.

pub fn despawn(&mut self, entity: Entity) -> bool

Free an entity’s slot. Returns whether it was alive to begin with.

Despawning an already-dead handle is a no-op rather than an error: it is the natural outcome of two systems both deciding something should go, and turning it into a failure would make every caller check first.

pub fn iter(&self) -> impl Iterator<Item = Entity> + '_

Every live entity, in ascending slot order.

The order is part of the contract, not an accident of the representation: see the crate docs.

Trait Implementations

impl Debug for Entities

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Entities

fn default() -> Entities

Returns the “default value” for a type.