Implement ExactSizeIterator for the other node types.

src/iter/ast_node_iter.rs

@@ -202,35 +202,14 @@ impl<'r, 's> AstNodeIter<'r, 's> {
     }
 }
 
-pub struct DocumentIter<'r, 's> {
+multi_field_iter!(
-    zeroth_section: std::option::Iter<'r, Section<'s>>,
+    Document<'s>,
-    children: std::slice::Iter<'r, Heading<'s>>,
+    DocumentIter,
-}
+    zeroth_section,
-impl<'r, 's> Iterator for DocumentIter<'r, 's> {
+    std::option::Iter<'r, Section<'s>>,
-    type Item = AstNode<'r, 's>;
+    children,
-    fn next(&mut self) -> Option<Self::Item> {
+    std::slice::Iter<'r, Heading<'s>>
-        self.zeroth_section
+);
-            .next()
-            .map(Into::<AstNode>::into)
-            .or_else(|| self.children.next().map(Into::<AstNode>::into))
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        let size = self.zeroth_section.len() + self.children.len();
-        (size, Some(size))
-    }
-}
-impl<'r, 's> ExactSizeIterator for DocumentIter<'r, 's> {}
-impl<'r, 's> IntoIterator for &'r Document<'s> {
-    type Item = AstNode<'r, 's>;
-    type IntoIter = DocumentIter<'r, 's>;
-    fn into_iter(self) -> Self::IntoIter {
-        DocumentIter {
-            zeroth_section: self.zeroth_section.iter(),
-            children: self.children.iter(),
-        }
-    }
-}
 multi_field_iter!(
     Heading<'s>,
     HeadingIter,

src/iter/macros.rs

@@ -11,7 +11,14 @@ macro_rules! children_iter {
             fn next(&mut self) -> Option<Self::Item> {
                 self.next.next().map(Into::<AstNode>::into)
             }
+
+            fn size_hint(&self) -> (usize, Option<usize>) {
+                let size = self.next.len();
+                (size, Some(size))
             }
+        }
+
+        impl<'r, 's> ExactSizeIterator for $itertype<'r, 's> {}
 
         impl<'r, 's> IntoIterator for &'r $astnodetype {
             type Item = AstNode<'r, 's>;
@@ -42,7 +49,13 @@ macro_rules! empty_iter {
             fn next(&mut self) -> Option<Self::Item> {
                 None
             }
+
+            fn size_hint(&self) -> (usize, Option<usize>) {
+                (0, Some(0))
             }
+        }
+
+        impl<'r, 's> ExactSizeIterator for $itertype<'r, 's> {}
 
         impl<'r, 's> IntoIterator for &'r $astnodetype {
             type Item = AstNode<'r, 's>;