Fix type of tombstone_traits::index. Fix tombstone_traits implementation for optional<T>

Author: davidstone

source/bounded/integer_tombstone_traits.cpp

@@ -48,11 +48,12 @@ struct tombstone_traits<T> {
 	}
 	static constexpr auto index(T const & value) noexcept {
 		auto const bounded_value = integer(value.m_value);
-		return
+		auto const result =
 			BOUNDED_CONDITIONAL(bounded_value < numeric_traits::min_value<T>, bounded_value - underlying_min,
 			BOUNDED_CONDITIONAL(bounded_value > numeric_traits::max_value<T>, bounded_value + spare_below - numeric_traits::max_value<T> - constant<1>,
 			constant<-1>
 		));
+		return bounded::assume_in_range(result, constant<-1>, spare_representations - constant<1>);
 	}
 };
 

source/bounded/tombstone_traits.cpp

@@ -5,7 +5,9 @@
 
 export module bounded.tombstone_traits;
 
+import bounded.arithmetic.operators;
 import bounded.integer;
+import bounded.normalize;
 
 namespace bounded {
 
@@ -35,9 +37,15 @@ struct tombstone_traits_composer<pointer> {
 	static constexpr auto spare_representations = tombstone_traits<Inner>::spare_representations;
 
 	static constexpr auto make(auto const index) noexcept -> Outer {
-		return Outer(tombstone_tag(), [=]() noexcept { return tombstone_traits<Inner>::make(index); });
+		return Outer(
+			tombstone_tag(),
+			[=] noexcept { return tombstone_traits<Inner>::make(index); }
+		);
 	}
-	static constexpr auto index(Outer const & value) noexcept {
+	static constexpr auto index(Outer const & value) noexcept -> bounded::integer<
+		-1,
+		bounded::normalize<spare_representations - bounded::constant<1>>
+	> {
 		return tombstone_traits<Inner>::index(value.*pointer);
 	}
 };

source/tv/optional.cpp

@@ -127,8 +127,17 @@ struct optional_storage<T> {
 		m_data(bounded::tombstone_traits<T>::make(index + 1_bi))
 	{
 	}
-	constexpr auto tombstone_index() const noexcept {
-		return bounded::tombstone_traits<T>::index(m_data) - 1_bi;
+	using tombstone_index_t = bounded::integer<
+		-1,
+		bounded::normalize<spare_representations - 1_bi>
+	>;
+	constexpr auto tombstone_index() const noexcept -> tombstone_index_t {
+		auto const underlying_index = bounded::tombstone_traits<T>::index(m_data);
+		return bounded::assume_in_range<tombstone_index_t>(
+			underlying_index == -1_bi ?
+				-1_bi :
+				underlying_index - 1_bi,
+		);
 	}
 
 private:

source/tv/test/optional.cpp

@@ -250,7 +250,7 @@ struct bounded::tombstone_traits<two_spare_representations> {
 	static constexpr auto make(auto const index) noexcept -> two_spare_representations {
 		return two_spare_representations{index == 0_bi ? 12 : 19};
 	}
-	static constexpr auto index(two_spare_representations const & value) noexcept {
+	static constexpr auto index(two_spare_representations const & value) noexcept -> bounded::integer<-1, 1> {
 		return
 			BOUNDED_CONDITIONAL(value.x == 12, 0_bi,
 			BOUNDED_CONDITIONAL(value.x == 19, 1_bi,