parser: use std::optional<T&> instead of T* in memo lookup return

Author: gf712

src/parser/Parser.cpp

@@ -133,8 +133,8 @@ template<typename Derived> struct PatternV2
 		if constexpr (seeds_sentinel) {
 			if (result.has_value()) {
 				// Safe to hold across grow_lr: memo entries live in a deque.
-				auto *slot = p.memo_find(start_position, memo_rule_id<Derived>);
-				ASSERT(slot);
+				const auto &slot = p.memo_find(start_position, memo_rule_id<Derived>);
+				ASSERT(slot.has_value());
 				ASSERT(slot->has_value());
 				auto &value = *slot;
 				if (std::holds_alternative<bool>(value->value) && std::get<bool>(value->value)) {
@@ -212,7 +212,8 @@ template<size_t TypeIdx, typename PatternTuple, typename = void> class PatternMa
 		if (!t.has_value()) { return {}; }
 		if constexpr (::detail::has_type<typename ResultTypeHead::value_type,
 						  ::detail::ValueTypesTuple>{}) {
-			if (auto *slot = p.memo_find(original_token_position, memo_rule_id<CurrentType>)) {
+			if (const auto &slot = p.memo_find(original_token_position, memo_rule_id<CurrentType>);
+				slot.has_value()) {
 				if (!slot->has_value()) { return {}; }
 				auto &value = (*slot)->value;
 				p.token_position() = (*slot)->position;

src/parser/Parser.cppm

@@ -25,18 +25,20 @@ class Parser
 
 	using MemoSlot = std::optional<CacheValue>;
 
-	MemoSlot *memo_find(std::size_t position, std::uint16_t rule)
+	std::optional<MemoSlot &> memo_find(std::size_t position, std::uint16_t rule)
 	{
-		if (position >= m_memo_index.size()) { return nullptr; }
+		if (position >= m_memo_index.size()) { return std::nullopt; }
 		for (const auto &[id, slot] : m_memo_index[position]) {
-			if (id == rule) { return &m_memo_pool[slot]; }
+			if (id == rule) { return m_memo_pool[slot]; }
 		}
-		return nullptr;
+		return std::nullopt;
 	}
 
 	MemoSlot &memo_insert(std::size_t position, std::uint16_t rule)
 	{
-		if (auto *existing = memo_find(position, rule)) { return *existing; }
+		if (const auto &existing = memo_find(position, rule); existing.has_value()) {
+			return existing.value();
+		}
 		if (position >= m_memo_index.size()) { m_memo_index.resize(position + 1); }
 		m_memo_pool.emplace_back();
 		m_memo_index[position].emplace_back(