Separate the lifetimes of each input of OrdMap::diff and OrdSet::diff (…

…#42)

This is a breaking change but only for code that uses turbofish syntax
on the `diff` method, the `DiffIter` type, or the `DiffItem` type.

Adapted from `im` PR #168.

Co-authored-by: Joe Neeman <[email protected]>

Co-authored-by: Simon Sapin <[email protected]>

src/nodes/btree.rs

@@ -1345,22 +1345,22 @@ impl<A: BTreeValue + Clone> ExactSizeIterator for ConsumingIter<A> {}
 // DiffIter
 
 /// An iterator over the differences between two ordered sets.
-pub struct DiffIter<'a, A> {
+pub struct DiffIter<'a, 'b, A> {
     old_stack: Vec<IterItem<'a, A>>,
-    new_stack: Vec<IterItem<'a, A>>,
+    new_stack: Vec<IterItem<'b, A>>,
 }
 
 /// A description of a difference between two ordered sets.
 #[derive(PartialEq, Eq, Debug)]
-pub enum DiffItem<'a, A> {
+pub enum DiffItem<'a, 'b, A> {
     /// This value has been added to the new set.
-    Add(&'a A),
+    Add(&'b A),
     /// This value has been changed between the two sets.
     Update {
         /// The old value.
         old: &'a A,
         /// The new value.
-        new: &'a A,
+        new: &'b A,
     },
     /// This value has been removed from the new set.
     Remove(&'a A),
@@ -1371,8 +1371,8 @@ enum IterItem<'a, A> {
     Yield(&'a A),
 }
 
-impl<'a, A: 'a> DiffIter<'a, A> {
-    pub(crate) fn new(old: &'a Node<A>, new: &'a Node<A>) -> Self {
+impl<'a, 'b, A: 'a + 'b> DiffIter<'a, 'b, A> {
+    pub(crate) fn new(old: &'a Node<A>, new: &'b Node<A>) -> Self {
         DiffIter {
             old_stack: if old.keys.is_empty() {
                 Vec::new()
@@ -1387,13 +1387,16 @@ impl<'a, A: 'a> DiffIter<'a, A> {
         }
     }
 
-    fn push_node(stack: &mut Vec<IterItem<'a, A>>, maybe_node: &'a Option<PoolRef<Node<A>>>) {
+    fn push_node<'either>(
+        stack: &mut Vec<IterItem<'either, A>>,
+        maybe_node: &'either Option<PoolRef<Node<A>>>,
+    ) {
         if let Some(node) = maybe_node {
             stack.push(IterItem::Consider(node))
         }
     }
 
-    fn push(stack: &mut Vec<IterItem<'a, A>>, node: &'a Node<A>) {
+    fn push<'either>(stack: &mut Vec<IterItem<'either, A>>, node: &'either Node<A>) {
         for n in 0..node.keys.len() {
             let i = node.keys.len() - n;
             Self::push_node(stack, &node.children[i]);
@@ -1403,11 +1406,11 @@ impl<'a, A: 'a> DiffIter<'a, A> {
     }
 }
 
-impl<'a, A> Iterator for DiffIter<'a, A>
+impl<'a, 'b, A> Iterator for DiffIter<'a, 'b, A>
 where
-    A: 'a + BTreeValue + PartialEq,
+    A: 'a + 'b + BTreeValue + PartialEq,
 {
-    type Item = DiffItem<'a, A>;
+    type Item = DiffItem<'a, 'b, A>;
 
     fn next(&mut self) -> Option<Self::Item> {
         loop {

src/ord/map.rs

@@ -399,7 +399,7 @@ where
     /// the two maps, minus the number of elements belonging to nodes
     /// shared between them)
     #[must_use]
-    pub fn diff<'a>(&'a self, other: &'a Self) -> DiffIter<'a, K, V> {
+    pub fn diff<'a, 'b>(&'a self, other: &'b Self) -> DiffIter<'a, 'b, K, V> {
         DiffIter {
             it: NodeDiffIter::new(&self.root, &other.root),
         }
@@ -1884,31 +1884,31 @@ where
 impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> where (K, V): 'a + BTreeValue {}
 
 /// An iterator over the differences between two maps.
-pub struct DiffIter<'a, K, V> {
-    it: NodeDiffIter<'a, (K, V)>,
+pub struct DiffIter<'a, 'b, K, V> {
+    it: NodeDiffIter<'a, 'b, (K, V)>,
 }
 
 /// A description of a difference between two ordered maps.
 #[derive(PartialEq, Eq, Debug)]
-pub enum DiffItem<'a, K, V> {
+pub enum DiffItem<'a, 'b, K, V> {
     /// This value has been added to the new map.
-    Add(&'a K, &'a V),
+    Add(&'b K, &'b V),
     /// This value has been changed between the two maps.
     Update {
         /// The old value.
         old: (&'a K, &'a V),
         /// The new value.
-        new: (&'a K, &'a V),
+        new: (&'b K, &'b V),
     },
     /// This value has been removed from the new map.
     Remove(&'a K, &'a V),
 }
 
-impl<'a, K, V> Iterator for DiffIter<'a, K, V>
+impl<'a, 'b, K, V> Iterator for DiffIter<'a, 'b, K, V>
 where
-    (K, V): 'a + BTreeValue + PartialEq,
+    (K, V): 'a + 'b + BTreeValue + PartialEq,
 {
-    type Item = DiffItem<'a, K, V>;
+    type Item = DiffItem<'a, 'b, K, V>;
 
     fn next(&mut self) -> Option<Self::Item> {
         self.it.next().map(|item| match item {

src/ord/set.rs

@@ -363,7 +363,7 @@ where
     /// the two sets, minus the number of elements belonging to nodes
     /// shared between them)
     #[must_use]
-    pub fn diff<'a>(&'a self, other: &'a Self) -> DiffIter<'_, A> {
+    pub fn diff<'a, 'b>(&'a self, other: &'b Self) -> DiffIter<'a, 'b, A> {
         DiffIter {
             it: NodeDiffIter::new(&self.root, &other.root),
         }
@@ -1028,15 +1028,15 @@ where
 }
 
 /// An iterator over the difference between two sets.
-pub struct DiffIter<'a, A> {
-    it: NodeDiffIter<'a, Value<A>>,
+pub struct DiffIter<'a, 'b, A> {
+    it: NodeDiffIter<'a, 'b, Value<A>>,
 }
 
-impl<'a, A> Iterator for DiffIter<'a, A>
+impl<'a, 'b, A> Iterator for DiffIter<'a, 'b, A>
 where
     A: Ord + PartialEq,
 {
-    type Item = DiffItem<'a, A>;
+    type Item = DiffItem<'a, 'b, A>;
 
     /// Advance the iterator and return the next value.
     ///