diff --git a/src/Partition.hxx b/src/Partition.hxx
index 237232810..59235c370 100644
--- a/src/Partition.hxx
+++ b/src/Partition.hxx
@@ -49,7 +49,7 @@ struct Partition final : QueueListener, PlayerListener, MixerListener {
 
 	std::unique_ptr<ClientListener> listener;
 
-	IntrusiveList<Client, ClientPerPartitionListHook, false> clients;
+	IntrusiveList<Client, ClientPerPartitionListHook> clients;
 
 	/**
 	 * Monitor for idle events local to this partition.
diff --git a/src/RemoteTagCache.hxx b/src/RemoteTagCache.hxx
index 96e59c0f2..fdaff2770 100644
--- a/src/RemoteTagCache.hxx
+++ b/src/RemoteTagCache.hxx
@@ -1,8 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 // Copyright The Music Player Daemon Project
 
-#ifndef MPD_REMOTE_TAG_CACHE_HXX
-#define MPD_REMOTE_TAG_CACHE_HXX
+#pragma once
 
 #include "input/RemoteTagScanner.hxx"
 #include "tag/Tag.hxx"
@@ -84,12 +83,13 @@ class RemoteTagCache final {
 	 */
 	ItemList invoke_list;
 
-	IntrusiveHashSet<Item, 127,
-			 IntrusiveHashSetOperators<std::hash<std::string_view>,
-						   std::equal_to<std::string_view>,
-						   Item::GetUri>,
-			 IntrusiveHashSetBaseHookTraits<Item>,
-			 true> map;
+	IntrusiveHashSet<
+		Item, 127,
+		IntrusiveHashSetOperators<std::hash<std::string_view>,
+					  std::equal_to<std::string_view>,
+					  Item::GetUri>,
+		IntrusiveHashSetBaseHookTraits<Item>,
+		IntrusiveHashSetOptions{.constant_time_size = true}> map;
 
 public:
 	RemoteTagCache(EventLoop &event_loop,
@@ -107,5 +107,3 @@ private:
 
 	void ItemResolved(Item &item) noexcept;
 };
-
-#endif
diff --git a/src/client/List.hxx b/src/client/List.hxx
index f5af653b6..6ee636035 100644
--- a/src/client/List.hxx
+++ b/src/client/List.hxx
@@ -1,15 +1,16 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 // Copyright The Music Player Daemon Project
 
-#ifndef MPD_CLIENT_LIST_HXX
-#define MPD_CLIENT_LIST_HXX
+#pragma once
 
 #include "Client.hxx"
 #include "util/IntrusiveList.hxx"
 
 class ClientList {
-	using List =
-		IntrusiveList<Client, IntrusiveListMemberHookTraits<&Client::list_siblings>, true>;
+	using List = IntrusiveList<
+		Client,
+		IntrusiveListMemberHookTraits<&Client::list_siblings>,
+		IntrusiveListOptions{.constant_time_size = true}>;
 
 	const unsigned max_size;
 
@@ -39,5 +40,3 @@ public:
 
 	void Remove(Client &client) noexcept;
 };
-
-#endif
diff --git a/src/output/plugins/httpd/HttpdInternal.hxx b/src/output/plugins/httpd/HttpdInternal.hxx
index 67eefe079..476508546 100644
--- a/src/output/plugins/httpd/HttpdInternal.hxx
+++ b/src/output/plugins/httpd/HttpdInternal.hxx
@@ -6,8 +6,7 @@
  * Internal declarations for the "httpd" audio output plugin.
  */
 
-#ifndef MPD_OUTPUT_HTTPD_INTERNAL_H
-#define MPD_OUTPUT_HTTPD_INTERNAL_H
+#pragma once
 
 #include "HttpdClient.hxx"
 #include "output/Interface.hxx"
@@ -121,8 +120,9 @@ private:
 	 * A linked list containing all clients which are currently
 	 * connected.
 	 */
-	IntrusiveList<HttpdClient, IntrusiveListBaseHookTraits<HttpdClient>,
-		      true> clients;
+	IntrusiveList<
+		HttpdClient, IntrusiveListBaseHookTraits<HttpdClient>,
+		IntrusiveListOptions{.constant_time_size = true}> clients;
 
 	/**
 	 * The maximum number of clients connected at the same time.
@@ -255,5 +255,3 @@ private:
 };
 
 extern const class Domain httpd_output_domain;
-
-#endif
diff --git a/src/util/IntrusiveForwardList.hxx b/src/util/IntrusiveForwardList.hxx
index 09e852dbe..2f3302064 100644
--- a/src/util/IntrusiveForwardList.hxx
+++ b/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 {
diff --git a/src/util/IntrusiveHashSet.hxx b/src/util/IntrusiveHashSet.hxx
index a1a252352..9bb535f80 100644
--- a/src/util/IntrusiveHashSet.hxx
+++ b/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;
 
diff --git a/src/util/IntrusiveList.hxx b/src/util/IntrusiveList.hxx
index aa1c67e55..54cab6933 100644
--- a/src/util/IntrusiveList.hxx
+++ b/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]]
diff --git a/src/util/IntrusiveSortedList.hxx b/src/util/IntrusiveSortedList.hxx
index cd029aa52..4cef8c099 100644
--- a/src/util/IntrusiveSortedList.hxx
+++ b/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;