From 848c2ff82ca81046acc0a8343b7892a7738f0af1 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Thu, 23 Mar 2017 19:34:43 +0200
Subject: [PATCH] Add fold expr implementations of mp_count, mp_count_if

---
 include/boost/mp11/detail/mp_count.hpp | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/include/boost/mp11/detail/mp_count.hpp b/include/boost/mp11/detail/mp_count.hpp
index 12bde18..ef97827 100644
--- a/include/boost/mp11/detail/mp_count.hpp
+++ b/include/boost/mp11/detail/mp_count.hpp
@@ -24,7 +24,14 @@ namespace detail
 
 template<class L, class V> struct mp_count_impl;
 
-#if !defined( BOOST_MP11_NO_CONSTEXPR )
+#if defined( BOOST_MP11_HAS_FOLD_EXPRESSIONS )
+
+template<template<class...> class L, class... T, class V> struct mp_count_impl<L<T...>, V>
+{
+    using type = mp_size_t<(std::is_same<T, V>::value + ... + 0)>;
+};
+
+#elif !defined( BOOST_MP11_NO_CONSTEXPR )
 
 constexpr std::size_t cx_plus()
 {
@@ -66,7 +73,14 @@ namespace detail
 
 template<class L, template<class...> class P> struct mp_count_if_impl;
 
-#if !defined( BOOST_MP11_NO_CONSTEXPR )
+#if defined( BOOST_MP11_HAS_FOLD_EXPRESSIONS )
+
+template<template<class...> class L, class... T, template<class...> class P> struct mp_count_if_impl<L<T...>, P>
+{
+    using type = mp_size_t<(mp_to_bool<P<T>>::value + ... + 0)>;
+};
+
+#elif !defined( BOOST_MP11_NO_CONSTEXPR )
 
 template<template<class...> class L, class... T, template<class...> class P> struct mp_count_if_impl<L<T...>, P>
 {