From efb719b8224254f7432679d3b74fae2c1286acc1 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Thu, 24 Aug 2017 14:39:06 +1000
Subject: [PATCH] coord/base: add indices method

---
 coord/base.hpp | 15 +++++++++++++++
 test/coord.cpp |  8 ++++++++
 2 files changed, 23 insertions(+)

diff --git a/coord/base.hpp b/coord/base.hpp
index 8a6dbc03..8a32ade2 100644
--- a/coord/base.hpp
+++ b/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]... };
+        }
     };
 }
 
diff --git a/test/coord.cpp b/test/coord.cpp
index 593cc0ec..8de918aa 100644
--- a/test/coord.cpp
+++ b/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 ();
 }