From ebd88b25e7284cbb293350d6898512ff89d5745d Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Mon, 24 Feb 2020 14:39:58 +1100
Subject: [PATCH] iterator/zip: use the `iterable` concept for zip construction

---
 iterator/zip.hpp | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/iterator/zip.hpp b/iterator/zip.hpp
index e5a4e095..cc07d2d0 100644
--- a/iterator/zip.hpp
+++ b/iterator/zip.hpp
@@ -9,6 +9,7 @@
 #pragma once
 
 #include "iota.hpp"
+#include "../concepts.hpp"
 #include "../tuple/value.hpp"
 #include "../variadic.hpp"
 #include "../functor.hpp"
@@ -81,6 +82,21 @@ namespace cruft::iterator {
             }
 
 
+            decltype (auto)
+            operator* (void) const
+            {
+                // We deliberately construct a tuple manually here to reduce
+                // the risk of dangling references. `forward_as_tuple` and
+                // `make_tuple` have resulted in references to locals in the
+                // past.
+                return std::tuple<
+                    decltype(*std::get<Indices> (m_iterators))...
+                > (
+                    *std::get<Indices> (m_iterators)...
+                );
+            }
+
+
             bool
             operator== (const zipped_iterator &rhs) const
             {
@@ -178,6 +194,7 @@ namespace cruft::iterator {
     ///
     /// eg, cruft::zip ({1,2,3}, {4,5,6}) ~= {{1,4},{2,5},{3,6}}
     template <typename ...ContainerT>
+    requires (cruft::concepts::iterable<ContainerT> && ...)
     decltype(auto)
     zip (ContainerT&&... data)
     {
@@ -199,6 +216,7 @@ namespace cruft::iterator {
     ///
     /// eg, cruft::izip ("abc") ~= {{0,'a'},{1,'b'},{2,'c'}}
     template <typename ...ContainerT>
+    requires (cruft::concepts::iterable<ContainerT> && ...)
     decltype(auto)
     izip (ContainerT&&... data)
     {