diff -r 8ff82697f2c3 -r 148b7c7ccaf9 src/cx/list.h
--- a/src/cx/list.h	Sat Jan 25 15:22:01 2025 +0100
+++ b/src/cx/list.h	Tue Jan 28 18:31:17 2025 +0100
@@ -165,7 +165,7 @@
     /**
      * Member function for finding and optionally removing an element.
      */
-    ssize_t (*find_remove)(
+    size_t (*find_remove)(
             struct cx_list_s *list,
             const void *elem,
             bool remove
@@ -362,6 +362,7 @@
         CxList *list,
         const void *elem
 ) {
+    list->collection.sorted = false;
     return list->cl->insert_element(list, list->collection.size, elem);
 }
 
@@ -387,6 +388,7 @@
         const void *array,
         size_t n
 ) {
+    list->collection.sorted = false;
     return list->cl->insert_array(list, list->collection.size, array, n);
 }
 
@@ -409,12 +411,15 @@
         size_t index,
         const void *elem
 ) {
+    list->collection.sorted = false;
     return list->cl->insert_element(list, index, elem);
 }
 
 /**
  * Inserts an item into a sorted list.
  *
+ * If the list is not sorted already, the behavior is undefined.
+ *
  * @param list the list
  * @param elem a pointer to the element to add
  * @retval zero success
@@ -425,6 +430,7 @@
         CxList *list,
         const void *elem
 ) {
+    list->collection.sorted = true; // guaranteed by definition
     const void *data = list->collection.store_pointer ? &elem : elem;
     return list->cl->insert_sorted(list, data, 1) == 0;
 }
@@ -455,6 +461,7 @@
         const void *array,
         size_t n
 ) {
+    list->collection.sorted = false;
     return list->cl->insert_array(list, index, array, n);
 }
 
@@ -470,6 +477,8 @@
  * If this list is storing pointers instead of objects @p array is expected to
  * be an array of pointers.
  *
+ * If the list is not sorted already, the behavior is undefined.
+ *
  * @param list the list
  * @param array a pointer to the elements to add
  * @param n the number of elements to add
@@ -481,6 +490,7 @@
         const void *array,
         size_t n
 ) {
+    list->collection.sorted = true; // guaranteed by definition
     return list->cl->insert_sorted(list, array, n);
 }
 
@@ -505,7 +515,9 @@
         CxIterator *iter,
         const void *elem
 ) {
-    return ((struct cx_list_s *) iter->src_handle.m)->cl->insert_iter(iter, elem, 0);
+    CxList* list = iter->src_handle.m;
+    list->collection.sorted = false;
+    return list->cl->insert_iter(iter, elem, 0);
 }
 
 /**
@@ -529,7 +541,9 @@
         CxIterator *iter,
         const void *elem
 ) {
-    return ((struct cx_list_s *) iter->src_handle.m)->cl->insert_iter(iter, elem, 1);
+    CxList* list = iter->src_handle.m;
+    list->collection.sorted = false;
+    return list->cl->insert_iter(iter, elem, 1);
 }
 
 /**
@@ -630,6 +644,7 @@
  */
 cx_attr_nonnull
 static inline void cxListClear(CxList *list) {
+    list->collection.sorted = true; // empty lists are always sorted
     list->cl->clear(list);
 }
 
@@ -652,6 +667,7 @@
         size_t i,
         size_t j
 ) {
+    list->collection.sorted = false;
     return list->cl->swap(list, i, j);
 }
 
@@ -819,12 +835,12 @@
  *
  * @param list the list
  * @param elem the element to find
- * @return the index of the element or a negative
- * value when the element is not found
+ * @return the index of the element or the size of the list when the element is not found
+ * @see cxListIndexValid()
  */
 cx_attr_nonnull
 cx_attr_nodiscard
-static inline ssize_t cxListFind(
+static inline size_t cxListFind(
         const CxList *list,
         const void *elem
 ) {
@@ -832,17 +848,32 @@
 }
 
 /**
+ * Checks if the specified index is within bounds.
+ *
+ * @param list the list
+ * @param index the index
+ * @retval true if the index is within bounds
+ * @retval false if the index is out of bounds
+ */
+cx_attr_nonnull
+cx_attr_nodiscard
+static inline bool cxListIndexValid(const CxList *list, size_t index) {
+    return index < list->collection.size;
+}
+
+/**
  * Removes and returns the index of the first element that equals @p elem.
  *
  * Determining equality is performed by the list's comparator function.
  *
  * @param list the list
  * @param elem the element to find and remove
- * @return the index of the now removed element or a negative
- * value when the element is not found or could not be removed
+ * @return the index of the now removed element or the list size
+ * when the element is not found or could not be removed
+ * @see cxListIndexValid()
  */
 cx_attr_nonnull
-static inline ssize_t cxListFindRemove(
+static inline size_t cxListFindRemove(
         CxList *list,
         const void *elem
 ) {
@@ -859,6 +890,7 @@
 cx_attr_nonnull
 static inline void cxListSort(CxList *list) {
     list->cl->sort(list);
+    list->collection.sorted = true;
 }
 
 /**
@@ -868,6 +900,8 @@
  */
 cx_attr_nonnull
 static inline void cxListReverse(CxList *list) {
+    // still sorted, but not according to the cmp_func
+    list->collection.sorted = false;
     list->cl->reverse(list);
 }