specialize: remove Boxes used by Children::insert

src/librustc/traits/specialize/specialization_graph.rs

@@ -132,10 +132,12 @@ impl<'a, 'gcx, 'tcx> Children {
  simplified_self,
  );
 
- for possible_sibling in match simplified_self {
- Some(sty) => self.filtered(sty),
- None => self.iter(),
- } {
+ let possible_siblings = match simplified_self {
+ Some(sty) => PotentialSiblings::Filtered(self.filtered(sty)),
+ None => PotentialSiblings::Unfiltered(self.iter()),
+ };
+
+ for possible_sibling in possible_siblings {
  debug!(
  "insert: impl_def_id={:?}, simplified_self={:?}, possible_sibling={:?}",
  impl_def_id,
@@ -222,14 +224,37 @@ impl<'a, 'gcx, 'tcx> Children {
  Ok(Inserted::BecameNewSibling(last_lint))
  }
 
- fn iter(&mut self) -> Box<dyn Iterator<Item = DefId> + '_> {
+ fn iter(&mut self) -> impl Iterator<Item = DefId> + '_ {
  let nonblanket = self.nonblanket_impls.iter_mut().flat_map(|(_, v)| v.iter());
- Box::new(self.blanket_impls.iter().chain(nonblanket).cloned())
+ self.blanket_impls.iter().chain(nonblanket).cloned()
  }
 
- fn filtered(&mut self, sty: SimplifiedType) -> Box<dyn Iterator<Item = DefId> + '_> {
+ fn filtered(&mut self, sty: SimplifiedType) -> impl Iterator<Item = DefId> + '_ {
  let nonblanket = self.nonblanket_impls.entry(sty).or_default().iter();
- Box::new(self.blanket_impls.iter().chain(nonblanket).cloned())
+ self.blanket_impls.iter().chain(nonblanket).cloned()
+ }
+}
+
+// A custom iterator used by Children::insert
+enum PotentialSiblings<I, J>
+ where I: Iterator<Item = DefId>,
+ J: Iterator<Item = DefId>
+{
+ Unfiltered(I),
+ Filtered(J)
+}
+
+impl<I, J> Iterator for PotentialSiblings<I, J>
+ where I: Iterator<Item = DefId>,
+ J: Iterator<Item = DefId>
+{
+ type Item = DefId;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ match *self {
+ PotentialSiblings::Unfiltered(ref mut iter) => iter.next(),
+ PotentialSiblings::Filtered(ref mut iter) => iter.next()
+ }
  }
 }