@@ -74,6 +74,58 @@ pub trait RelationshipSourceCollection {
7474 }
7575}
7676
77+ /// This trait signals that a [`RelationshipSourceCollection`] is ordered.
78+ pub trait OrderedRelationshipSourceCollection : RelationshipSourceCollection {
79+ /// Inserts the entity at a specific index.
80+ /// If the index is too large, the entity will be added to the end of the collection.
81+ fn insert ( & mut self , index : usize , entity : Entity ) ;
82+ /// Removes the entity at the specified idnex if it exists.
83+ fn remove_at ( & mut self , index : usize ) -> Option < Entity > ;
84+ /// Inserts the entity at a specific index.
85+ /// This will never reorder other entities.
86+ /// If the index is too large, the entity will be added to the end of the collection.
87+ fn insert_stable ( & mut self , index : usize , entity : Entity ) ;
88+ /// Removes the entity at the specified idnex if it exists.
89+ /// This will never reorder other entities.
90+ fn remove_at_stable ( & mut self , index : usize ) -> Option < Entity > ;
91+ /// Sorts the source collection.
92+ fn sort ( & mut self ) ;
93+ /// Inserts the entity at the proper place to maintain sorting.
94+ fn insert_sorted ( & mut self , entity : Entity ) ;
95+
96+ /// This places the most recently added entity at the particular index.
97+ fn place_most_recent ( & mut self , index : usize ) ;
98+
99+ /// This places the given entity at the particular index.
100+ /// This will do nothing if the entity is not in the collection.
101+ /// If the index is out of bounds, this will put the entity at the end.
102+ fn place ( & mut self , entity : Entity , index : usize ) ;
103+
104+ /// Adds the entity at index 0.
105+ fn push_front ( & mut self , entity : Entity ) {
106+ self . insert ( 0 , entity) ;
107+ }
108+
109+ /// Adds the entity to the back of the collection.
110+ fn push_back ( & mut self , entity : Entity ) {
111+ self . insert ( usize:: MAX , entity) ;
112+ }
113+
114+ /// Removes the first entity.
115+ fn pop_front ( & mut self ) -> Option < Entity > {
116+ self . remove_at ( 0 )
117+ }
118+
119+ /// Removes the last entity.
120+ fn pop_back ( & mut self ) -> Option < Entity > {
121+ if self . is_empty ( ) {
122+ None
123+ } else {
124+ self . remove_at ( self . len ( ) - 1 )
125+ }
126+ }
127+ }
128+
77129impl RelationshipSourceCollection for Vec < Entity > {
78130 type SourceIter < ' a > = core:: iter:: Copied < core:: slice:: Iter < ' a , Entity > > ;
79131
@@ -98,7 +150,6 @@ impl RelationshipSourceCollection for Vec<Entity> {
98150 fn remove ( & mut self , entity : Entity ) -> bool {
99151 if let Some ( index) = <[ Entity ] >:: iter ( self ) . position ( |e| * e == entity) {
100152 Vec :: remove ( self , index) ;
101-
102153 return true ;
103154 }
104155
@@ -126,6 +177,57 @@ impl RelationshipSourceCollection for Vec<Entity> {
126177 }
127178}
128179
180+ impl OrderedRelationshipSourceCollection for Vec < Entity > {
181+ fn insert ( & mut self , index : usize , entity : Entity ) {
182+ self . push ( entity) ;
183+ let len = self . len ( ) ;
184+ if index < len {
185+ self . swap ( index, len - 1 ) ;
186+ }
187+ }
188+
189+ fn remove_at ( & mut self , index : usize ) -> Option < Entity > {
190+ ( index < self . len ( ) ) . then ( || self . swap_remove ( index) )
191+ }
192+
193+ fn insert_stable ( & mut self , index : usize , entity : Entity ) {
194+ if index < self . len ( ) {
195+ Vec :: insert ( self , index, entity) ;
196+ } else {
197+ self . push ( entity) ;
198+ }
199+ }
200+
201+ fn remove_at_stable ( & mut self , index : usize ) -> Option < Entity > {
202+ ( index < self . len ( ) ) . then ( || self . remove ( index) )
203+ }
204+
205+ fn sort ( & mut self ) {
206+ self . sort_unstable ( ) ;
207+ }
208+
209+ fn insert_sorted ( & mut self , entity : Entity ) {
210+ let index = self . partition_point ( |e| e <= & entity) ;
211+ self . insert_stable ( index, entity) ;
212+ }
213+
214+ fn place_most_recent ( & mut self , index : usize ) {
215+ if let Some ( entity) = self . pop ( ) {
216+ let index = index. min ( self . len ( ) - 1 ) ;
217+ self . insert ( index, entity) ;
218+ }
219+ }
220+
221+ fn place ( & mut self , entity : Entity , index : usize ) {
222+ if let Some ( current) = <[ Entity ] >:: iter ( self ) . position ( |e| * e == entity) {
223+ // The len is at least 1, so the subtraction is safe.
224+ let index = index. min ( self . len ( ) - 1 ) ;
225+ Vec :: remove ( self , current) ;
226+ self . insert ( index, entity) ;
227+ } ;
228+ }
229+ }
230+
129231impl RelationshipSourceCollection for EntityHashSet {
130232 type SourceIter < ' a > = core:: iter:: Copied < crate :: entity:: hash_set:: Iter < ' a > > ;
131233
@@ -196,7 +298,6 @@ impl<const N: usize> RelationshipSourceCollection for SmallVec<[Entity; N]> {
196298 fn remove ( & mut self , entity : Entity ) -> bool {
197299 if let Some ( index) = <[ Entity ] >:: iter ( self ) . position ( |e| * e == entity) {
198300 SmallVec :: remove ( self , index) ;
199-
200301 return true ;
201302 }
202303
@@ -277,6 +378,57 @@ impl RelationshipSourceCollection for Entity {
277378 }
278379}
279380
381+ impl < const N : usize > OrderedRelationshipSourceCollection for SmallVec < [ Entity ; N ] > {
382+ fn insert ( & mut self , index : usize , entity : Entity ) {
383+ self . push ( entity) ;
384+ let len = self . len ( ) ;
385+ if index < len {
386+ self . swap ( index, len - 1 ) ;
387+ }
388+ }
389+
390+ fn remove_at ( & mut self , index : usize ) -> Option < Entity > {
391+ ( index < self . len ( ) ) . then ( || self . swap_remove ( index) )
392+ }
393+
394+ fn insert_stable ( & mut self , index : usize , entity : Entity ) {
395+ if index < self . len ( ) {
396+ SmallVec :: < [ Entity ; N ] > :: insert ( self , index, entity) ;
397+ } else {
398+ self . push ( entity) ;
399+ }
400+ }
401+
402+ fn remove_at_stable ( & mut self , index : usize ) -> Option < Entity > {
403+ ( index < self . len ( ) ) . then ( || self . remove ( index) )
404+ }
405+
406+ fn sort ( & mut self ) {
407+ self . sort_unstable ( ) ;
408+ }
409+
410+ fn insert_sorted ( & mut self , entity : Entity ) {
411+ let index = self . partition_point ( |e| e <= & entity) ;
412+ self . insert_stable ( index, entity) ;
413+ }
414+
415+ fn place_most_recent ( & mut self , index : usize ) {
416+ if let Some ( entity) = self . pop ( ) {
417+ let index = index. min ( self . len ( ) - 1 ) ;
418+ self . insert ( index, entity) ;
419+ }
420+ }
421+
422+ fn place ( & mut self , entity : Entity , index : usize ) {
423+ if let Some ( current) = <[ Entity ] >:: iter ( self ) . position ( |e| * e == entity) {
424+ // The len is at least 1, so the subtraction is safe.
425+ let index = index. min ( self . len ( ) - 1 ) ;
426+ SmallVec :: < [ Entity ; N ] > :: remove ( self , current) ;
427+ self . insert ( index, entity) ;
428+ } ;
429+ }
430+ }
431+
280432#[ cfg( test) ]
281433mod tests {
282434 use super :: * ;
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