From 84963aacf80c27a606bf4cbcf503c2af1d3348c5 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Thu, 24 Aug 2017 14:32:58 +1000
Subject: [PATCH] coord/ops: make 'all' and 'any' constexpr

---
 coord/ops.hpp  | 70 +++++++++++++++++++++++++++++++++++++++++++-------
 test/coord.cpp | 12 +++++++++
 2 files changed, 73 insertions(+), 9 deletions(-)

diff --git a/coord/ops.hpp b/coord/ops.hpp
index c02a8700..2e488311 100644
--- a/coord/ops.hpp
+++ b/coord/ops.hpp
@@ -899,38 +899,90 @@ namespace util {
 #undef SCALAR_OP
 
 
-    //-------------------------------------------------------------------------
+    ///////////////////////////////////////////////////////////////////////////
+    namespace detail {
+        template <
+            std::size_t S,
+            template <std::size_t,typename> class K,
+            std::size_t ...I,
+            typename = std::enable_if_t<
+                is_coord_v<K<S,bool>>,
+                void
+            >
+        >
+        constexpr bool
+        any (const K<S,bool> k, std::index_sequence<I...>)
+        {
+            return (k[I] || ...);
+        }
+    };
+
+
+    ///---------------------------------------------------------------------------
+    /// returns true if any element is true.
+    ///
+    /// this function must be suitable for use in static_assert, so it must remain
+    /// constexpr.
+    ///
+    /// we would ideally use std::any_of, but it is not constexpr.
+    /// we would ideally use range-for, but cbegin is not constexpr.
+    /// so... moar templates.
     template <
         size_t S,
         template <size_t,typename> class K,
         typename = std::enable_if_t<
             is_coord_v<K<S,bool>>, void
-        >
+        >,
+        typename Indices = std::make_index_sequence<S>
     >
     constexpr
     bool
     any (const K<S,bool> k)
     {
-        return std::any_of (std::cbegin (k),
-                            std::cend   (k),
-                            identity<bool>);
+        return detail::any (k, Indices{});
+    }
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    namespace detail {
+        template <
+            std::size_t S,
+            template <size_t,typename> class K,
+            std::size_t ...I,
+            typename = std::enable_if_t<
+                is_coord_v<K<S,bool>>,
+                void
+            >
+        >
+        constexpr bool
+        all (const K<S,bool> k, std::index_sequence<I...>)
+        {
+            return (k[I] && ...);
+        }
     }
 
     //-------------------------------------------------------------------------
+    /// returns true if all elements are true.
+    ///
+    /// this function must be suitable for use in static_assert, so it must be
+    /// constexpr.
+    ///
+    /// we would ideally use std::all_of, but it is not constexpr.
+    /// we would ideally use range-for, but cbegin is not constexpr.
+    /// so... moar templates.
     template <
         size_t S,
         template <size_t,typename> class K,
         typename = std::enable_if_t<
             is_coord_v<K<S,bool>>, void
-        >
+        >,
+        typename Indices = std::make_index_sequence<S>
     >
     constexpr
     bool
     all (const K<S,bool> k)
     {
-        return std::all_of (std::cbegin (k),
-                            std::cend   (k),
-                            identity<bool>);
+        return detail::all (k, Indices {});
     }
 
 
diff --git a/test/coord.cpp b/test/coord.cpp
index c2b9f183..593cc0ec 100644
--- a/test/coord.cpp
+++ b/test/coord.cpp
@@ -54,6 +54,18 @@ main (void)
         );
     }
 
+    // test expected outputs for various logical operations
+    {
+        constexpr util::point3i a {  0, -1,  2 };
+        constexpr util::point3i b {  0,  1, -2 };
+        constexpr util::point3i c { -9, -9, -9 };
+
+        tap.expect (!all (a <= b), "all, expected failure");
+        tap.expect ( all (a <= a), "all, expected success");
+        tap.expect (!any (a <= c), "any, expected failure");
+        tap.expect ( any (a <= b), "any, expected success");
+    };
+
     // ensure the util::select function behaves as expected
     {
         const util::point3f a { -1, 2, 0 };