fixes for MSVC and nvc++

- MSVC finds the get(...) member function, so we need to call the free function explicitly
- the structured bindings refer to a reference

Author: upsj

core/base/iterator_factory.hpp

@@ -13,6 +13,8 @@
 #include <tuple>
 #include <utility>
 
+#include <ginkgo/core/base/types.hpp>
+
 #include "core/base/copy_assignable.hpp"
 
 
@@ -290,15 +292,15 @@ class zip_iterator_reference
         // std::tuple<int, char> t = { 1, '2' }; is not allowed.
         // converting to 'std::tuple<...>' from initializer list would use
         // explicit constructor
-        return value_type(get<idxs>(*this)...);
+        return value_type(gko::get<idxs>(*this)...);
     }
 
     template <std::size_t... idxs>
     constexpr void assign_impl(std::index_sequence<idxs...>,
                                const value_type& other)
     {
         (void)std::initializer_list<int>{
-            (get<idxs>(*this) = get<idxs>(other), 0)...};
+            (gko::get<idxs>(*this) = gko::get<idxs>(other), 0)...};
     }
 
     constexpr explicit zip_iterator_reference(Iterators... it)
@@ -509,7 +511,7 @@ class zip_iterator {
         auto other_it = get<0>(other.iterators_);
         auto result = fn(it, other_it);
         forall_impl(
-            other, [&](auto a, auto b) { assert(it - other_it == a - b); },
+            other, [&](auto a, auto b) { GKO_ASSERT(it - other_it == a - b); },
             index_sequence{});
         return result;
     }

test/base/iterator_factory.cpp

@@ -52,7 +52,8 @@ void run_zip_iterator(std::shared_ptr<gko::EXEC_TYPE> exec,
             }
             // check structured bindings
             auto [key, value] = *begin;
-            static_assert(std::is_same<typeof(key), int>::value,
+            static_assert(std::is_same<std::remove_reference_t<decltype(key)>,
+                                       int>::value,
                           "incorrect type");
             gko::get<0>(*begin) = value;
         },