[OTLayout] More templatizing Extension

src/hb-ot-layout-gpos-table.hh

@@ -1248,12 +1248,7 @@ struct ChainContextPos : ChainContext {};
 
 struct ExtensionPos : Extension<ExtensionPos>
 {
-  inline const struct PosLookupSubTable& get_subtable (void) const
-  {
-    unsigned int offset = get_offset ();
-    if (unlikely (!offset)) return Null(PosLookupSubTable);
-    return StructAtOffset<PosLookupSubTable> (this, offset);
-  }
+  typedef struct PosLookupSubTable LookupSubTable;
 
   inline bool sanitize (hb_sanitize_context_t *c);
 };

src/hb-ot-layout-gsub-table.hh

@@ -880,12 +880,7 @@ struct ChainContextSubst : ChainContext {};
 
 struct ExtensionSubst : Extension<ExtensionSubst>
 {
-  inline const struct SubstLookupSubTable& get_subtable (void) const
-  {
-    unsigned int offset = get_offset ();
-    if (unlikely (!offset)) return Null(SubstLookupSubTable);
-    return StructAtOffset<SubstLookupSubTable> (this, offset);
-  }
+  typedef struct SubstLookupSubTable LookupSubTable;
 
   inline bool sanitize (hb_sanitize_context_t *c);
 
@@ -1390,7 +1385,7 @@ inline bool ExtensionSubst::is_reverse (void) const
 {
   unsigned int type = get_type ();
   if (unlikely (type == SubstLookupSubTable::Extension))
-    return CastR<ExtensionSubst> (get_subtable()).is_reverse ();
+    return CastR<ExtensionSubst> (get_subtable<SubstLookupSubTable>()).is_reverse ();
   return SubstLookup::lookup_type_is_reverse (type);
 }
 

src/hb-ot-layout-gsubgpos-private.hh

@@ -1783,10 +1783,18 @@ struct Extension
     }
   }
 
+  template <typename X>
+  inline const X& get_subtable (void) const
+  {
+    unsigned int offset = get_offset ();
+    if (unlikely (!offset)) return Null(typename T::LookupSubTable);
+    return StructAtOffset<typename T::LookupSubTable> (this, offset);
+  }
+
   template <typename context_t>
   inline typename context_t::return_t process (context_t *c) const
   {
-    return CastP<T>(this)->get_subtable ().process (c, get_type ());
+    return CastP<T>(this)->get_subtable<typename T::LookupSubTable> ().process (c, get_type ());
   }
 
   inline bool sanitize (hb_sanitize_context_t *c) {