From 619003d1d414167630331efffe83702f74413be6 Mon Sep 17 00:00:00 2001
From: Phlosioneer <mattmdrr2@gmail.com>
Date: Tue, 20 Mar 2018 05:33:59 -0400
Subject: Implement some trivial size_hints for various iterators

This also implements ExactSizeIterator where applicable.

Addresses most of the Iterator traits mentioned in #23708.
---
 src/librustc_data_structures/graph/mod.rs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

(limited to 'src/librustc_data_structures/graph')

diff --git a/src/librustc_data_structures/graph/mod.rs b/src/librustc_data_structures/graph/mod.rs
index 1945b82c031..e2b393071ff 100644
--- a/src/librustc_data_structures/graph/mod.rs
+++ b/src/librustc_data_structures/graph/mod.rs
@@ -334,6 +334,11 @@ impl<'g, N: Debug, E: Debug> Iterator for AdjacentEdges<'g, N, E> {
         self.next = edge.next_edge[self.direction.repr];
         Some((edge_index, edge))
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        // At most, all the edges in the graph.
+        (0, Some(self.graph.len_edges()))
+    }
 }
 
 pub struct DepthFirstTraversal<'g, N, E>
@@ -383,8 +388,16 @@ impl<'g, N: Debug, E: Debug> Iterator for DepthFirstTraversal<'g, N, E> {
         }
         next
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        // We will visit every node in the graph exactly once.
+        let remaining = self.graph.len_nodes() - self.visited.count();
+        (remaining, Some(remaining))
+    }
 }
 
+impl<'g, N: Debug, E: Debug> ExactSizeIterator for DepthFirstTraversal<'g, N, E> {}
+
 impl<E> Edge<E> {
     pub fn source(&self) -> NodeIndex {
         self.source
-- 
cgit 1.4.1-3-g733a5