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

source/mijin/container/optional.hpp

@@ -138,6 +138,10 @@ public:
     constexpr explicit operator bool() const noexcept { return !empty(); }
     [[nodiscard]]
     constexpr bool operator !() const noexcept { return empty(); }
+    [[nodiscard]]
+    constexpr std::remove_reference_t<TValue>& operator*() noexcept { return get(); }
+    [[nodiscard]]
+    constexpr const std::remove_reference_t<TValue>& operator*() const noexcept { return get(); }
 public:
     template<typename... Types>
     void emplace(Types&&... params) noexcept;