diff -r bb18daa62d5f -r b0ebb3d88407 src/cx/compare.h
--- a/src/cx/compare.h	Sat Dec 30 18:48:25 2023 +0100
+++ b/src/cx/compare.h	Sun Dec 31 14:29:46 2023 +0100
@@ -42,6 +42,17 @@
 extern "C" {
 #endif
 
+#ifndef CX_COMPARE_FUNC_DEFINED
+#define CX_COMPARE_FUNC_DEFINED
+/**
+ * A comparator function comparing two collection elements.
+ */
+typedef int(*cx_compare_func)(
+        void const *left,
+        void const *right
+);
+#endif // CX_COMPARE_FUNC_DEFINED
+
 /**
  * Compares two integers of type int.
  *