[iter] Accept iterator, not iterable, in hb_sink()()

src/hb-iter.hh

@@ -371,12 +371,12 @@ struct hb_sink_t
 {
   hb_sink_t (Sink&& s) : s (s) {}
 
-  template <typename Iterable,
-	    hb_enable_if (hb_is_iterable (Iterable))>
+  template <typename Iter,
+	    hb_enable_if (hb_is_iterator (Iter))>
   void
-  operator () (const Iterable &c) const
+  operator () (Iter it) const
   {
-    for (auto it = c.iter (); it; ++it)
+    for (; it; ++it)
       s << *it;
   }
 

src/test-iter.cc

@@ -145,6 +145,7 @@ main (int argc, char **argv)
   | hb_filter ()
   | hb_filter (hb_bool)
   | hb_filter (hb_bool, hb_identity)
+  | hb_sink (st)
   ;
 
   t << 1;