Struct bevy_ecs::query::QueryCombinationIter
source · pub struct QueryCombinationIter<'w, 's, Q: WorldQuery, F: ReadOnlyWorldQuery, const K: usize> { /* private fields */ }
Expand description
An iterator over K
-sized combinations of query items without repetition.
A combination is an arrangement of a collection of items where order does not matter.
K
is the number of items that make up each subset, and the number of items returned by the iterator.
N
is the number of total entities output by the query.
For example, given the list [1, 2, 3, 4], where K
is 2, the combinations without repeats are
[1, 2], [1, 3], [1, 4], [2, 3], [2, 4], [3, 4].
And in this case, N
would be defined as 4 since the size of the input list is 4.
The number of combinations depend on how K
relates to the number of entities matching the Query
:
- if
K = N
, only one combination exists, - if
K < N
, there are NCK combinations (see the performance section ofQuery
), - if
K > N
, there are no combinations.
The output combination is not guaranteed to have any order of iteration.
Usage
This type is returned by calling Query::iter_combinations
or Query::iter_combinations_mut
.
It implements Iterator
only if it iterates over read-only query items (learn more).
In the case of mutable query items, it can be iterated by calling fetch_next
in a while let
loop.
Examples
The following example shows how to traverse the iterator when the query items are read-only.
fn some_system(query: Query<&ComponentA>) {
for [a1, a2] in query.iter_combinations() {
// ...
}
}
The following example shows how fetch_next
should be called with a while let
loop to traverse the iterator when the query items are mutable.
fn some_system(mut query: Query<&mut ComponentA>) {
let mut combinations = query.iter_combinations_mut();
while let Some([a1, a2]) = combinations.fetch_next() {
// ...
}
}
Implementations§
source§impl<'w, 's, Q: WorldQuery, F: ReadOnlyWorldQuery, const K: usize> QueryCombinationIter<'w, 's, Q, F, K>
impl<'w, 's, Q: WorldQuery, F: ReadOnlyWorldQuery, const K: usize> QueryCombinationIter<'w, 's, Q, F, K>
sourcepub fn fetch_next(&mut self) -> Option<[Q::Item<'_>; K]>
pub fn fetch_next(&mut self) -> Option<[Q::Item<'_>; K]>
Get next combination of queried components
Trait Implementations§
source§impl<'w, 's, Q: ReadOnlyWorldQuery, F: ReadOnlyWorldQuery, const K: usize> Iterator for QueryCombinationIter<'w, 's, Q, F, K>
impl<'w, 's, Q: ReadOnlyWorldQuery, F: ReadOnlyWorldQuery, const K: usize> Iterator for QueryCombinationIter<'w, 's, Q, F, K>
§type Item = [<Q as WorldQuery>::Item<'w>; K]
type Item = [<Q as WorldQuery>::Item<'w>; K]
source§fn next(&mut self) -> Option<Self::Item>
fn next(&mut self) -> Option<Self::Item>
source§fn size_hint(&self) -> (usize, Option<usize>)
fn size_hint(&self) -> (usize, Option<usize>)
source§fn next_chunk<const N: usize>(
&mut self
) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>where
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fn next_chunk<const N: usize>(
&mut self
) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>where
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Self: Sized,
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fn nth(&mut self, n: usize) -> Option<Self::Item>
n
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Auto Trait Implementations§
impl<'w, 's, Q, F, const K: usize> !RefUnwindSafe for QueryCombinationIter<'w, 's, Q, F, K>
impl<'w, 's, Q, F, const K: usize> !Send for QueryCombinationIter<'w, 's, Q, F, K>
impl<'w, 's, Q, F, const K: usize> !Sync for QueryCombinationIter<'w, 's, Q, F, K>
impl<'w, 's, Q, F, const K: usize> Unpin for QueryCombinationIter<'w, 's, Q, F, K>where
Q: Unpin,
<F as WorldQuery>::Fetch<'w>: Unpin,
<Q as WorldQuery>::Fetch<'w>: Unpin,
impl<'w, 's, Q, F, const K: usize> !UnwindSafe for QueryCombinationIter<'w, 's, Q, F, K>
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