pub fn Optional<'a, T, C, S>(
component_ref: &'a S,
) -> OptionalQueryItem<'a, T, S>
Expand description
Helper func to construct a OptionalQueryItem
wrapping a Comp
SystemParam
.
Used to iterate over enities optionally retrieving components from ComponentStore
.
Entities iterated over will not be filtered by this QueryItem
.
This example filters entities by compC
, optionally retrieves compA
as mutable, and
compB
as immutable. (OptionalMut
is used for mutation).
entities.iter_with(&mut OptionalMut(&mut compA), &Optional(&compB), &compC)
This will implement QueryItem
as long as generic type implements std::ops::Deref
for
ComponentStore
, such as Comp
and CompMut
.