coord/base: add std::array conversion operator

coord/base.hpp

@@ -25,6 +25,7 @@
 #include "../maths.hpp"
 
 #include <algorithm>
+#include <array>
 #include <cstdlib>
 #include <type_traits>
 
@@ -104,6 +105,7 @@ namespace util::coord {
         const T& back (void) const { return this->data[S-1]; }
         T& back (void) { return this->data[S-1]; }
 
+
         ///////////////////////////////////////////////////////////////////////
         // conversions
         template <template <std::size_t, typename> class K>
@@ -142,6 +144,16 @@ namespace util::coord {
             return out;
         }
 
+
+        ///////////////////////////////////////////////////////////////////////
+        operator std::array<value_type,elements> () const
+        {
+            std::array<value_type,elements> res;
+            std::copy (begin (), end (), std::begin (res));
+            return res;
+        }
+
+
         ///////////////////////////////////////////////////////////////////////
         /// returns an instance with the same data, but truncated to `D'
         /// elements

test/coord.cpp

@@ -42,6 +42,15 @@ main (void)
         tap.expect (x == p.x && y == p.y, "structured bindings extract correct data");
     }
 
+    // check that we can assign to arrays from coord types
+    {
+        std::array<int,2> q = p;
+        tap.expect (
+            std::equal (std::begin (q), std::end (q), std::begin (p)),
+            "assignment to array preserves values"
+        );
+    }
+
     // ensure the distance function behaves correctly with non-normal numbers.
     {
         util::point3f a { 103, 0, 14 };