Struct specs::join::MaybeJoin

pub struct MaybeJoin<J: Join>(pub J);

A Join-able structure that yields all indices, returning None for all missing elements and Some(T) for found elements.

For usage see Join::maybe().

WARNING: Do not have a join of only MaybeJoins. Otherwise the join will iterate over every single index of the bitset. If you want a join with all MaybeJoins, add an EntitiesRes to the join as well to bound the join to all entities that are alive.

Trait Implementations

impl<T> Join for MaybeJoin<T> where
    T: Join, 

type Mask = BitSetAll

Type of joined bit mask.

type Type = Option<<T as Join>::Type>

Type of joined components.

type Value = (<T as Join>::Mask, <T as Join>::Value)

Type of joined storages.

unsafe fn open(self) -> (Self::Mask, Self::Value)

Open this join by returning the mask and the storages.

unsafe fn get((mask, value): &mut Self::Value, id: Index) -> Self::Type

Get a joined component value by a given index.

fn is_unconstrained() -> bool

If this Join typically returns all indices in the mask, then iterating over only it or combined with other joins that are also dangerous will cause the JoinIter/ParJoin to go through all indices which is usually not what is wanted and will kill performance.

Important traits for JoinIter<J>

impl<J: Join> Iterator for JoinIter<J> type Item = J::Type;

fn join(self) -> JoinIter<Self> where
    Self: Sized, 

Create a joined iterator over the contents.

fn maybe(self) -> MaybeJoin<Self> where
    Self: Sized, 

Returns a Join-able structure that yields all indices, returning None for all missing elements and Some(T) for found elements.