Added operators to BoxedObject, fixed MappintIterator for reference types and fixed signature of custom assertion and error handlers.

source/mijin/util/iterators.hpp

@@ -10,6 +10,7 @@
 #include <string_view>
 #include <tuple>
 #include <variant>
+#include "../container/optional.hpp"
 
 namespace mijin
 {
@@ -277,7 +278,7 @@ struct MappingIterator
 {
     using orig_value_type = typename std::iterator_traits<TIterator>::value_type;
     using difference_type = std::ptrdiff_t;
-    using value_type = std::invoke_result_t<TFunctor, orig_value_type>;
+    using value_type = std::invoke_result_t<TFunctor, orig_value_type&>;
     using reference = value_type&;
     using iterator_category = std::bidirectional_iterator_tag; // TODO?
 
@@ -285,7 +286,7 @@ struct MappingIterator
 
     TIterator base;
     TFunctor functor;
-    mutable std::optional<value_type> result;
+    mutable Optional<value_type> result;
 
     MappingIterator(TIterator base_, TFunctor functor_) noexcept : base(base_), functor(std::move(functor_)) {}
     MappingIterator(const MappingIterator&) noexcept = default;
@@ -296,8 +297,8 @@ struct MappingIterator
 
     reference operator*() const noexcept
     {
-        if (!result.has_value()) {
-            result = functor(*base);
+        if (result.empty()) {
+            result = std::invoke(functor, *base);
         }
         return *result;
     }
@@ -305,7 +306,7 @@ struct MappingIterator
     MappingIterator& operator++() noexcept
     {
         ++base;
-        result = std::nullopt;
+        result.reset();
         return *this;
     }
 
@@ -319,7 +320,7 @@ struct MappingIterator
     MappingIterator& operator--() noexcept
     {
         --base;
-        result = std::nullopt;
+        result.reset();
         return *this;
     }