util/Intrusive*: move constant_time_size to an options struct

This makes it easier to add more options later.

src/util/IntrusiveForwardList.hxx

@@ -14,6 +14,10 @@
 #include <type_traits>
 #include <utility>
 
+struct IntrusiveForwardListOptions {
+	bool constant_time_size = false;
+};
+
 struct IntrusiveForwardListNode {
 	IntrusiveForwardListNode *next;
 };
@@ -93,8 +97,10 @@ struct IntrusiveForwardListMemberHookTraits {
  */
 template<typename T,
 	 typename HookTraits=IntrusiveForwardListBaseHookTraits<T>,
-	 bool constant_time_size=false>
+	 IntrusiveForwardListOptions options=IntrusiveForwardListOptions{}>
 class IntrusiveForwardList {
+	static constexpr bool constant_time_size = options.constant_time_size;
+
 	IntrusiveForwardListNode head{nullptr};
 
 	[[no_unique_address]]
@@ -145,7 +151,7 @@ public:
 		:head(src.head)
 	{
 		// shallow copies mess with the counter
-		static_assert(!constant_time_size);
+		static_assert(!options.constant_time_size);
 	}
 
 	IntrusiveForwardList &operator=(IntrusiveForwardList &&src) noexcept {

src/util/IntrusiveHashSet.hxx

@@ -10,6 +10,10 @@
 #include <array>
 #include <numeric> // for std::accumulate()
 
+struct IntrusiveHashSetOptions {
+	bool constant_time_size = false;
+};
+
 template<IntrusiveHookMode mode=IntrusiveHookMode::NORMAL>
 struct IntrusiveHashSetHook {
 	using SiblingsHook = IntrusiveListHook<mode>;
@@ -106,8 +110,10 @@ struct IntrusiveHashSetOperators {
 template<typename T, std::size_t table_size,
 	 typename Operators,
 	 typename HookTraits=IntrusiveHashSetBaseHookTraits<T>,
-	 bool constant_time_size=false>
+	 IntrusiveHashSetOptions options=IntrusiveHashSetOptions{}>
 class IntrusiveHashSet {
+	static constexpr bool constant_time_size = options.constant_time_size;
+
 	[[no_unique_address]]
 	OptionalCounter<constant_time_size> counter;
 

src/util/IntrusiveList.hxx

@@ -13,6 +13,10 @@
 #include <type_traits>
 #include <utility>
 
+struct IntrusiveListOptions {
+	bool constant_time_size = false;
+};
+
 struct IntrusiveListNode {
 	IntrusiveListNode *next, *prev;
 
@@ -27,7 +31,7 @@ template<IntrusiveHookMode _mode=IntrusiveHookMode::NORMAL>
 class IntrusiveListHook {
 	template<typename T> friend struct IntrusiveListBaseHookTraits;
 	template<auto member> friend struct IntrusiveListMemberHookTraits;
-	template<typename T, typename HookTraits, bool> friend class IntrusiveList;
+	template<typename T, typename HookTraits, IntrusiveListOptions> friend class IntrusiveList;
 
 protected:
 	IntrusiveListNode siblings;
@@ -135,8 +139,10 @@ struct IntrusiveListMemberHookTraits {
  */
 template<typename T,
 	 typename HookTraits=IntrusiveListBaseHookTraits<T>,
-	 bool constant_time_size=false>
+	 IntrusiveListOptions options=IntrusiveListOptions{}>
 class IntrusiveList {
+	static constexpr bool constant_time_size = options.constant_time_size;
+
 	IntrusiveListNode head{&head, &head};
 
 	[[no_unique_address]]

src/util/IntrusiveSortedList.hxx

@@ -14,11 +14,11 @@
  */
 template<typename T, typename Compare=typename T::Compare,
 	 typename HookTraits=IntrusiveListBaseHookTraits<T>,
-	 bool constant_time_size=false>
+	 IntrusiveListOptions options=IntrusiveListOptions{}>
 class IntrusiveSortedList
-	: public IntrusiveList<T, HookTraits, constant_time_size>
+	: public IntrusiveList<T, HookTraits, options>
 {
-	using Base = IntrusiveList<T, HookTraits, constant_time_size>;
+	using Base = IntrusiveList<T, HookTraits, options>;
 
 	[[no_unique_address]]
 	Compare compare;