From 5aa2cd5eb9292cc2354267063e9170c1cbb91ec5 Mon Sep 17 00:00:00 2001
From: Jason Rhinelander <jason@imaginary.ca>
Date: Thu, 8 Sep 2016 17:45:53 -0400
Subject: [PATCH] Template simplifications

Switch count_t to use constexpr_sum (under non-MSVC), and then make
all_of_t/any_of_t use it instead of doing the sum itself.

For MSVC, count_t is still done using template recursion, but
all_of_t/any_of_t can also make use of it.
---
 include/pybind11/common.h | 29 ++++++++++++-----------------
 1 file changed, 12 insertions(+), 17 deletions(-)

diff --git a/include/pybind11/common.h b/include/pybind11/common.h
index c086e8796..255cc79a3 100644
--- a/include/pybind11/common.h
+++ b/include/pybind11/common.h
@@ -342,22 +342,24 @@ constexpr size_t constexpr_sum() { return 0; }
 template <typename T, typename... Ts>
 constexpr size_t constexpr_sum(T n, Ts... ns) { return size_t{n} + constexpr_sum(ns...); }
 
-/// Return true if all/any Ts satify Predicate<T>
+// Counts the number of types in the template parameter pack matching the predicate
 #if !defined(_MSC_VER)
 template <template<typename> class Predicate, typename... Ts>
-using all_of_t = bool_constant<(constexpr_sum(Predicate<Ts>::value...) == sizeof...(Ts))>;
-template <template<typename> class Predicate, typename... Ts>
-using any_of_t = bool_constant<(constexpr_sum(Predicate<Ts>::value...) > 0)>;
+using count_t = std::integral_constant<size_t, constexpr_sum(Predicate<Ts>::value...)>;
 #else
 // MSVC workaround (2015 Update 3 has issues with some member type aliases and constexpr)
-template <template<typename> class P, typename...> struct all_of_t : std::true_type { };
-template <template<typename> class P, typename T, typename... Ts>
-struct all_of_t<P, T, Ts...> : conditional_t<P<T>::value, all_of_t<P, Ts...>, std::false_type> { };
-template <template<typename> class P, typename...> struct any_of_t : std::false_type { };
-template <template<typename> class P, typename T, typename... Ts>
-struct any_of_t<P, T, Ts...> : conditional_t<P<T>::value, std::true_type, any_of_t<P, Ts...>> { };
+template <template<typename> class Predicate, typename... Ts> struct count_t;
+template <template<typename> class Predicate> struct count_t<Predicate> : std::integral_constant<size_t, 0> {};
+template <template<typename> class Predicate, class T, class... Ts>
+struct count_t<Predicate, T, Ts...> : std::integral_constant<size_t, Predicate<T>::value + count_t<Predicate, Ts...>::value> {};
 #endif
 
+/// Return true if all/any Ts satify Predicate<T>
+template <template<typename> class Predicate, typename... Ts>
+using all_of_t = bool_constant<(count_t<Predicate, Ts...>::value == sizeof...(Ts))>;
+template <template<typename> class Predicate, typename... Ts>
+using any_of_t = bool_constant<(count_t<Predicate, Ts...>::value > 0)>;
+
 // Extracts the first type from the template parameter pack matching the predicate, or Default if none match.
 template <template<class> class Predicate, class Default, class... Ts> struct first_of;
 template <template<class> class Predicate, class Default> struct first_of<Predicate, Default> {
@@ -373,13 +375,6 @@ struct first_of<Predicate, Default, T, Ts...> {
 };
 template <template<class> class Predicate, class Default, class... T> using first_of_t = typename first_of<Predicate, Default, T...>::type;
 
-// Counts the number of types in the template parameter pack matching the predicate
-template <template<typename> class Predicate, typename... Ts> struct count_t;
-template <template<typename> class Predicate> struct count_t<Predicate> : std::integral_constant<size_t, 0> {};
-template <template<typename> class Predicate, class T, class... Ts>
-struct count_t<Predicate, T, Ts...> : std::integral_constant<size_t,
-    Predicate<T>::value + count_t<Predicate, Ts...>::value> {};
-
 /// Defer the evaluation of type T until types Us are instantiated
 template <typename T, typename... /*Us*/> struct deferred_type { using type = T; };
 template <typename T, typename... Us> using deferred_t = typename deferred_type<T, Us...>::type;