[librsvg: 1/9] node.rs: Impl DoubleEndedIterator for Children

[Federico Mena Quintero <federico src gnome org>]

commit dc61a094f0bc67f023a5179710fbb23326320407
Author: Ivan Molodetskikh <yalterz gmail com>
Date:   Thu Mar 15 20:51:12 2018 +0300

    node.rs: Impl DoubleEndedIterator for Children

 rsvg_internals/src/node.rs | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)
---
diff --git a/rsvg_internals/src/node.rs b/rsvg_internals/src/node.rs
index ae7a59f4..c14af5a7 100644
--- a/rsvg_internals/src/node.rs
+++ b/rsvg_internals/src/node.rs
@@ -72,6 +72,7 @@ pub struct Node {
 pub struct Children<'a> {
     children: Ref<'a, Vec<Rc<Node>>>,
     index: usize,
+    reverse_index: usize,
 }
 
 // Keep this in sync with rsvg-private.h:RsvgNodeType
@@ -293,7 +294,12 @@ pub fn boxed_node_new(
 
 impl<'a> Children<'a> {
     fn new(children: Ref<'a, Vec<Rc<Node>>>) -> Self {
-        Self { children, index: 0 }
+        let len = children.len();
+        Self {
+            children,
+            index: 0,
+            reverse_index: len,
+        }
     }
 }
 
@@ -301,7 +307,7 @@ impl<'a> Iterator for Children<'a> {
     type Item = Rc<Node>;
 
     fn next(&mut self) -> Option<Self::Item> {
-        if self.index == self.children.len() {
+        if self.index == self.reverse_index {
             return None;
         }
 
@@ -311,11 +317,22 @@ impl<'a> Iterator for Children<'a> {
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        let count = self.children.len() - self.index;
+        let count = self.reverse_index - self.index;
         (count, Some(count))
     }
 }
 
+impl<'a> DoubleEndedIterator for Children<'a> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        if self.index == self.reverse_index {
+            return None;
+        }
+
+        self.reverse_index -= 1;
+        Some(self.children[self.reverse_index].clone())
+    }
+}
+
 impl<'a> ExactSizeIterator for Children<'a> {}
 
 #[no_mangle]