[iter] Add hb_iter_with_mixin_t<>

src/hb-array.hh

@@ -38,8 +38,9 @@ struct hb_sorted_array_t;
 
 template <typename Type>
 struct hb_array_t :
-	hb_iter_t<hb_array_t<Type>, Type&>,
-	hb_iter_fallback_mixin_t<hb_array_t<Type>, Type&>
+  hb_iter_with_mixin_t<hb_iter_fallback_mixin_t,
+		       hb_array_t<Type>,
+		       Type&>
 {
   /*
    * Constructors.

src/hb-iter.hh

@@ -132,6 +132,19 @@ template <typename Type, unsigned int length> hb_array_t<Type>
 hb_iter (Type (&array)[length]) { return hb_iter (array, length); }
 
 
+template <template<typename iter_t, typename item_t> class mixin_t,
+	  typename iter_t,
+	  typename item_t = typename iter_t::__item_t__>
+struct hb_iter_with_mixin_t :
+  hb_iter_t<iter_t, item_t>,
+  mixin_t<iter_t, item_t>
+{
+  protected:
+  hb_iter_with_mixin_t () {}
+  hb_iter_with_mixin_t (const hb_iter_with_mixin_t &o HB_UNUSED) {}
+  void operator = (const hb_iter_with_mixin_t &o HB_UNUSED) {}
+};
+
 /* Mixin to fill in what the subclass doesn't provide. */
 template <typename iter_t, typename item_t = typename iter_t::__item_t__>
 struct hb_iter_fallback_mixin_t
@@ -270,8 +283,9 @@ hb_map (Proj&& f)
 template <typename Iter, typename Pred, typename Proj,
 	 hb_enable_if (hb_is_iterator (Iter))>
 struct hb_filter_iter_t :
-  hb_iter_t<hb_filter_iter_t<Iter, Pred, Proj>, typename Iter::item_t>,
-  hb_iter_fallback_mixin_t<hb_filter_iter_t<Iter, Pred, Proj>, typename Iter::item_t>
+  hb_iter_with_mixin_t<hb_iter_fallback_mixin_t,
+		       hb_filter_iter_t<Iter, Pred, Proj>,
+		       typename Iter::item_t>
 {
   hb_filter_iter_t (const Iter& it_, Pred&& p, Proj&& f) : it (it_), p (p), f (f)
   { while (it && !p (f (*it))) ++it; }

src/hb-ot-layout-common.hh

@@ -1121,8 +1121,9 @@ struct Coverage
   }
 
   struct iter_t :
-    hb_iter_t<iter_t, hb_codepoint_t>,
-    hb_iter_fallback_mixin_t<iter_t, hb_codepoint_t>
+    hb_iter_with_mixin_t<hb_iter_fallback_mixin_t,
+			 iter_t,
+			 hb_codepoint_t>
   {
     static constexpr bool is_sorted_iterator = true;
     iter_t (const Coverage &c_ = Null(Coverage))

src/hb-set.hh

@@ -683,8 +683,9 @@ struct hb_set_t
    * Iterator implementation.
    */
   struct iter_t :
-    hb_iter_t<iter_t, hb_codepoint_t>,
-    hb_iter_fallback_mixin_t<iter_t, hb_codepoint_t>
+    hb_iter_with_mixin_t<hb_iter_fallback_mixin_t,
+			 iter_t,
+			 hb_codepoint_t>
   {
     static constexpr bool is_sorted_iterator = true;
     iter_t (const hb_set_t &s_ = Null(hb_set_t)) :

src/test-iter.cc

@@ -34,8 +34,9 @@
 
 template <typename T>
 struct array_iter_t :
-  hb_iter_t<array_iter_t<T>, T&>,
-  hb_iter_fallback_mixin_t<array_iter_t<T>, T&>
+  hb_iter_with_mixin_t<hb_iter_fallback_mixin_t,
+		       array_iter_t<T>,
+		       T&>
 {
   array_iter_t (hb_array_t<T> arr_) : arr (arr_) {}