From ff68be31bf2ea82bf6bfcc6f993fb6806a895f97 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Tue, 16 Apr 2019 09:59:08 -0400
Subject: [PATCH] Add hb_void_tt<> ala std::void_t

---
 src/hb-meta.hh | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/hb-meta.hh b/src/hb-meta.hh
index a71121991..d2733d716 100644
--- a/src/hb-meta.hh
+++ b/src/hb-meta.hh
@@ -90,6 +90,13 @@ static T&& hb_forward (hb_remove_reference (T)&& t) { return (T&&) t; }
 /* Void!  For when we need a expression-type of void. */
 struct hb_void_t { typedef void value; };
 
+/* Void meta-function ala std::void_t
+ * https://en.cppreference.com/w/cpp/types/void_t */
+template<typename... Ts>
+struct _hb_make_void { typedef void type; };
+template<typename... Ts>
+using hb_void_tt = typename _hb_make_void<Ts...>::type;
+
 /* Bool!  For when we need to evaluate type-dependent expressions
  * in a template argument. */
 template <bool b> struct hb_bool_tt { enum { value = b }; };