Redirect size_hint method to the underlying iterators

src/window.rs

@@ -445,9 +445,14 @@ pub struct PollEventsIterator<'a>(winimpl::PollEventsIterator<'a>);
 
 impl<'a> Iterator for PollEventsIterator<'a> {
     type Item = Event;
+
     fn next(&mut self) -> Option<Event> {
         self.0.next()
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.0.size_hint()
+    }
 }
 
 /// An iterator for the `wait_events` function.
@@ -455,9 +460,14 @@ pub struct WaitEventsIterator<'a>(winimpl::WaitEventsIterator<'a>);
 
 impl<'a> Iterator for WaitEventsIterator<'a> {
     type Item = Event;
+
     fn next(&mut self) -> Option<Event> {
         self.0.next()
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.0.size_hint()
+    }
 }
 
 /// An iterator for the list of available monitors.
@@ -469,9 +479,14 @@ pub struct AvailableMonitorsIter {
 
 impl Iterator for AvailableMonitorsIter {
     type Item = MonitorID;
+
     fn next(&mut self) -> Option<MonitorID> {
         self.data.next().map(|id| MonitorID(id))
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.data.size_hint()
+    }
 }
 
 /// Returns the list of all available monitors.