coord/base: add indices method

coord/base.hpp

@@ -160,6 +160,21 @@ namespace util::coord {
             std::fill (next, std::end (out), fill);
             return out;
         }
+
+
+        ///////////////////////////////////////////////////////////////////////
+        /// returns an instance with elements specified by the Indices
+        /// parameter. eg, point2f p{}.indices<0,2> would return {p.x, p.z}.
+        ///
+        /// it's ugly as sin, but simplifies some situations where we don't
+        /// want a temporary.
+        template <std::size_t ...Indices>
+        KLASS<sizeof...(Indices),T>
+        indices (void) const
+        {
+            static_assert (all (make_vector ((Indices < S)...)));
+            return KLASS<sizeof...(Indices),T> { this->data[Indices]... };
+        }
     };
 }
 

test/coord.cpp

@@ -91,5 +91,13 @@ main (void)
         tap.expect_eq (limit (val, 0.f, 2.f), util::vector3f { 0, 0, 2 }, "limit with vec/num/num");
     }
 
+    // ensure that klass::indices appears to link correctly
+    {
+        const util::vector3i seq { 0, 1, 2 };
+        const util::vector4i res { 2, 0, 0, 1 };
+
+        tap.expect_eq (seq.indices<2,0,0,1> (), res, "coord::indices expansion");
+    };
+
     return tap.status ();
 }