Self-execute closures for assert() (#46)

diff --git a/lib/src/differs/list_differ.dart b/lib/src/differs/list_differ.dart
index bcb0dfd..ab0e5c2 100644
--- a/lib/src/differs/list_differ.dart
+++ b/lib/src/differs/list_differ.dart
@@ -306,7 +306,7 @@
   assert(() {
     splices = new List<ListChangeRecord<E>>.unmodifiable(splices);
     return true;
-  });
+  }());
   return splices;
 }
 
diff --git a/lib/src/internal.dart b/lib/src/internal.dart
index 780e317..d600f50 100644
--- a/lib/src/internal.dart
+++ b/lib/src/internal.dart
@@ -7,6 +7,6 @@
   assert(() {
     list = new List<E>.unmodifiable(list);
     return true;
-  });
+  }());
   return list;
 }
diff --git a/lib/src/records/list_change_record.dart b/lib/src/records/list_change_record.dart
index 8b8c41e..0ebdb43 100644
--- a/lib/src/records/list_change_record.dart
+++ b/lib/src/records/list_change_record.dart
@@ -95,7 +95,7 @@
         throw new ArgumentError('Invalid `addedCount`: $addedCount');
       }
       return true;
-    });
+    }());
   }
 
   /// Returns whether [reference] index was changed in this operation.