From 8128632f1aa4db1a2ec6de8f89ce401b09a29e8a Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Sat, 10 Aug 2024 14:19:25 +1000
Subject: [PATCH] iterator/zip: allow ranges with differing begin/end types

---
 cruft/util/iterator/zip.hpp | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/cruft/util/iterator/zip.hpp b/cruft/util/iterator/zip.hpp
index b02e15fc..1eae3f02 100644
--- a/cruft/util/iterator/zip.hpp
+++ b/cruft/util/iterator/zip.hpp
@@ -26,6 +26,16 @@ namespace cruft::iterator {
         class zipped_iterator;
 
 
+        template <typename T>
+        struct zipped_reference { using type = void; };
+
+        template <typename KlassT>
+            requires requires { typename KlassT::reference; }
+        struct zipped_reference<KlassT> {
+            using type = KlassT::reference;
+        };
+
+
         template <
             typename IteratorT,
             std::size_t ...IndexV
@@ -46,9 +56,12 @@ namespace cruft::iterator {
             using difference_type = std::ptrdiff_t;
 
             using value_type = std::tuple<
-                typename std::iterator_traits<
-                    std::tuple_element_t<IndexV, IteratorT>
-                >::reference...
+                // Because std::default_sentinel_t doesn't have iterator members
+                typename zipped_reference<
+                    typename std::iterator_traits<
+                        std::tuple_element_t<IndexV, IteratorT>
+                    >
+                >::type...
             >;
 
             using reference = value_type;
@@ -107,11 +120,11 @@ namespace cruft::iterator {
                 );
             }
 
-
+            template <typename OtherT, typename OtherIndexV>
             bool
-            operator== (zipped_iterator const &rhs) const
+            operator== (zipped_iterator<OtherT, OtherIndexV> const &rhs) const
             {
-                return m_iterators == rhs.m_iterators;
+                return m_iterators == rhs.inner ();
             }
 
 
@@ -121,6 +134,7 @@ namespace cruft::iterator {
                 return !(*this == rhs);
             }
 
+            auto const& inner (void) const& { return m_iterators; }
 
         private:
             IteratorT m_iterators;