xo-arena: + ArenaHashMapConfig with functional mutators

include/xo/arena/ArenaHashMapConfig.hpp

@@ -0,0 +1,58 @@
+/** @file ArenaHashMapConfig.hpp
+ *
+ *  @author Roland Conybeare, Feb 2026
+ **/
+
+#pragma once
+
+#include <string>
+#include <cstdint>
+
+namespace xo {
+    namespace map {
+        /** @class ArenaHashMapConfig
+         *
+         *  @brief configuration for a @ref DArenaHashMap instance
+         **/
+        struct ArenaHashMapConfig {
+            /** @defgroup map-arenahashmapconfig-ctors **/
+            ///@{
+
+            ArenaHashMapConfig with_name(std::string name) const {
+                ArenaHashMapConfig copy(*this);
+                copy.name_ = name;
+                return copy;
+            }
+
+            ArenaHashMapConfig with_hint_max_capacity(std::size_t z) const {
+                ArenaHashMapConfig copy(*this);
+                copy.hint_max_capacity_ = z;
+                return copy;
+            }
+
+            ArenaHashMapConfig with_debug_flag(bool x) const {
+                ArenaHashMapConfig copy(*this);
+                copy.debug_flag_ = x;
+                return copy;
+            }
+
+            ///@}
+            /** @defgroup mm-arenahashmapconfig-instance-vars ArenaHashMapConfig members **/
+            ///@{
+
+            /** optional name, for diagnostics **/
+            std::string name_;
+            /** desired hard max hashmap size -> reserved virtual memory
+             *  hint: actual max may be larger, because of power-of-2 considerations.
+             **/
+            std::size_t hint_max_capacity_ = 0;
+            /** true to enable debug logging **/
+            bool debug_flag_ = false;
+
+            ///@}
+        };
+
+    } /*namespace map*/
+} /*namespace xo*/
+
+/* end ArenaHashMapConfig.hpp */