From b14745278ad16fe7f4e838b685029e3fdda516ca Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Fri, 10 May 2019 21:42:59 -0700
Subject: [PATCH] [met]a Add is_constructible, ...

---
 src/hb-meta.hh   | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/test-meta.cc | 23 ++++++++++++++++++
 2 files changed, 96 insertions(+)

diff --git a/src/hb-meta.hh b/src/hb-meta.hh
index f676231..0ab7179 100644
--- a/src/hb-meta.hh
+++ b/src/hb-meta.hh
@@ -292,4 +292,77 @@ template <> struct hb_int_max<unsigned long long>	: hb_integral_constant<unsigne
 #define hb_int_max(T) hb_int_max<T>::value
 
 
+template <typename T, typename, typename ...Ts>
+struct _hb_is_constructible : hb_false_type {};
+template <typename T, typename ...Ts>
+struct _hb_is_constructible<T, hb_void_t<decltype (T (hb_declval (Ts)...))>, Ts...> : hb_true_type {};
+template <typename T, typename ...Ts>
+using hb_is_constructible = _hb_is_constructible<T, void, Ts...>;
+#define hb_is_constructible(...) hb_is_constructible<__VA_ARGS__>::value
+
+template <typename T>
+using hb_is_default_constructible = hb_is_constructible<T>;
+#define hb_is_default_constructible(T) hb_is_default_constructible<T>::value
+
+template <typename T>
+using hb_is_copy_constructible = hb_is_constructible<T, hb_add_lvalue_reference<hb_add_const<T>>>;
+#define hb_is_copy_constructible(T) hb_is_copy_constructible<T>::value
+
+template <typename T>
+using hb_is_move_constructible = hb_is_constructible<T, hb_add_rvalue_reference<hb_add_const<T>>>;
+#define hb_is_move_constructible(T) hb_is_move_constructible<T>::value
+
+template <typename T, typename U, typename>
+struct _hb_is_assignable : hb_false_type {};
+template <typename T, typename U>
+struct _hb_is_assignable<T, U, hb_void_t<decltype (hb_declval (T) = hb_declval (U))>> : hb_true_type {};
+template <typename T, typename U>
+using hb_is_assignable = _hb_is_assignable<T, U, void>;
+#define hb_is_assignable(T,U) hb_is_assignable<T, U>::value
+
+template <typename T>
+using hb_is_copy_assignable = hb_is_assignable<hb_add_lvalue_reference<T>,
+					       hb_add_lvalue_reference<hb_add_const<T>>>;
+#define hb_is_copy_assignable(T) hb_is_copy_assignable<T>::value
+
+template <typename T>
+using hb_is_move_assignable = hb_is_assignable<hb_add_lvalue_reference<T>,
+					       hb_add_rvalue_reference<T>>;
+#define hb_is_move_assignable(T) hb_is_move_assignable<T>::value
+
+/* Trivial versions. */
+
+template <typename T> union hb_trivial { T value; };
+
+/* Don't know how to do the following. */
+//template <typename T, typename ...Ts>
+//using hb_is_trivially_constructible= hb_is_constructible<hb_trivial<T>, hb_trivial<Ts>...>;
+//#define hb_is_trivially_constructible(...) hb_is_trivially_constructible<__VA_ARGS__>::value
+
+template <typename T>
+using hb_is_trivially_default_constructible= hb_is_default_constructible<hb_trivial<T>>;
+#define hb_is_trivially_default_constructible(T) hb_is_trivially_default_constructible<T>::value
+
+template <typename T>
+using hb_is_trivially_copy_constructible= hb_is_copy_constructible<hb_trivial<T>>;
+#define hb_is_trivially_copy_constructible(T) hb_is_trivially_copy_constructible<T>::value
+
+template <typename T>
+using hb_is_trivially_move_constructible= hb_is_move_constructible<hb_trivial<T>>;
+#define hb_is_trivially_move_constructible(T) hb_is_trivially_move_constructible<T>::value
+
+/* Don't know how to do the following. */
+//template <typename T, typename U>
+//using hb_is_trivially_assignable= hb_is_assignable<hb_trivial<T>, hb_trivial<U>>;
+//#define hb_is_trivially_assignable(T,U) hb_is_trivially_assignable<T, U>::value
+
+template <typename T>
+using hb_is_trivially_copy_assignable= hb_is_copy_assignable<hb_trivial<T>>;
+#define hb_is_trivially_copy_assignable(T) hb_is_trivially_copy_assignable<T>::value
+
+template <typename T>
+using hb_is_trivially_move_assignable= hb_is_move_assignable<hb_trivial<T>>;
+#define hb_is_trivially_move_assignable(T) hb_is_trivially_move_assignable<T>::value
+
+
 #endif /* HB_META_HH */
diff --git a/src/test-meta.cc b/src/test-meta.cc
index 6fb8e4f..af1ca2e 100644
--- a/src/test-meta.cc
+++ b/src/test-meta.cc
@@ -27,6 +27,8 @@
 #include "hb.hh"
 #include "hb-meta.hh"
 
+#include <type_traits>
+
 
 int
 main (int argc, char **argv)
@@ -94,5 +96,26 @@ main (int argc, char **argv)
   static_assert (hb_is_base_of (X, const Y), "");
   static_assert (!hb_is_base_of (Y, X), "");
 
+  static_assert (hb_is_constructible (int), "");
+  static_assert (hb_is_constructible (int, int), "");
+  static_assert (hb_is_constructible (int, char), "");
+  static_assert (hb_is_constructible (int, long), "");
+  static_assert (!hb_is_constructible (int, X), "");
+  static_assert (!hb_is_constructible (int, int, int), "");
+  static_assert (hb_is_constructible (X), "");
+  static_assert (!hb_is_constructible (X, int), "");
+  static_assert (hb_is_constructible (X, X), "");
+  static_assert (!hb_is_constructible (X, X, X), "");
+  static_assert (hb_is_constructible (X, Y), "");
+  static_assert (!hb_is_constructible (Y, X), "");
+
+  static_assert (hb_is_trivially_default_constructible (X), "");
+  static_assert (hb_is_trivially_default_constructible (Y), "");
+  static_assert (hb_is_trivially_copy_constructible (X), "");
+  static_assert (hb_is_trivially_copy_constructible (Y), "");
+  static_assert (hb_is_trivially_move_constructible (X), "");
+  static_assert (hb_is_trivially_move_constructible (Y), "");
+  /* TODO Add more meaningful tests. */
+
   return 0;
 }
-- 
2.7.4