From 061088467fc1cfc578f19eed05c7fc49bbb5a368 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Thu, 15 Jun 2017 16:24:44 +1000
Subject: [PATCH] coord: add structured bindings support

---
 coord/ops.hpp  | 107 +++++++++++++++++++++++++++++++++++++++++++++++++
 test/coord.cpp |   7 ++++
 2 files changed, 114 insertions(+)

diff --git a/coord/ops.hpp b/coord/ops.hpp
index dcf0afa6..e66a945c 100644
--- a/coord/ops.hpp
+++ b/coord/ops.hpp
@@ -864,6 +864,113 @@ namespace util {
                         floor_func);
         return out;
     }
+
+    /// returns the data at a templated index in a coordinate.
+    ///
+    /// specifically required for structured bindings support.
+    ///
+    /// \tparam I index of the requested data
+    /// \tparam S dimensionality of the coordinate
+    /// \tparam T underlying data type of the coordinate
+    /// \tparam K coordinate data type to operate on
+    template <
+        size_t I,
+        size_t S,
+        typename T,
+        template<
+        size_t,
+        typename
+    > class K
+    >
+    const std::enable_if_t<
+        is_coord_v<K<S,T>>,
+        T
+    >&
+    get (const K<S,T> &k)
+    {
+        static_assert (I < S);
+        return k[I];
+    };
+
+
+    /// returns the data at a templated index in a coordinate.
+    ///
+    /// specifically required for structured bindings support.
+    ///
+    /// \tparam I index of the requested data
+    /// \tparam S dimensionality of the coordinate
+    /// \tparam T underlying data type of the coordinate
+    /// \tparam K coordinate data type to operate on
+    template <
+        size_t I,
+        size_t S,
+        typename T,
+        template<
+            size_t,
+            typename
+        > class K
+    >
+    std::enable_if_t<
+        is_coord_v<K<S,T>>,
+        T
+    >&
+    get (K<S,T> &k)
+    {
+        static_assert (I < S);
+        return k[I];
+    };
 }
 
+
+#include <tuple>
+
+
+namespace std {
+    /// returns the dimensions of a coordinate type.
+    ///
+    /// specifically required for structured bindings support.
+    ///
+    /// \tparam S dimensions
+    /// \tparam T data type
+    /// \tparam K coordinate class
+    template <
+        size_t S,
+        typename T,
+        template<
+            size_t,
+            typename
+        > class K
+    >
+    class tuple_size<K<S,T>> : public std::enable_if_t<
+        ::util::is_coord_v<K<S,T>>,
+        std::integral_constant<decltype(S), S>
+    > { };
+
+
+    /// indicates the type at a given index of a coordinate type
+    ///
+    /// specifically required for structured bindings support.
+    ///
+    /// \tparam I data index
+    /// \tparam S dimensionality of the coordinate
+    /// \tparam T data type for the coordinate
+    /// \tparam K the underlying coordinate class
+    template <
+        size_t I,
+        size_t S,
+        typename T,
+        template<
+            size_t,
+            typename
+        > class K
+    >
+    class tuple_element<
+        I, K<S,T>
+    > : public enable_if<
+        ::util::is_coord_v<K<S,T>>,
+        T
+    > { };
+}
+
+
 #endif
diff --git a/test/coord.cpp b/test/coord.cpp
index cdc860b2..d9c4d9b0 100644
--- a/test/coord.cpp
+++ b/test/coord.cpp
@@ -36,5 +36,12 @@ main (void)
 
     tap.expect_eq (sum (util::vector4f::ones ()), 4.f, "elementwise summation");
 
+    // check that structured bindings work
+    {
+        const auto &[x,y] = p;
+        tap.expect (x == p.x && y == p.y, "structured bindings extract correct data");
+    }
+
+
     return tap.status ();
 }