xo-alloc: + ArenaAllocT for use with std::map() etc.

include/xo/alloc/ArenaAllocT.hpp

@@ -0,0 +1,74 @@
+/** @file Allocator.hpp
+ *
+ *  @author Roland Conybeare, Nov 2025
+ **/
+
+#pragma once
+
+#include "xo/alloc/ArenaAlloc.hpp"
+
+namespace xo {
+    namespace gc {
+        /** @class allocator
+         *  @brief c++ allocator with allocator traits
+         *
+         *  Can use ArenaAllocT with std::map etc.
+         **/
+        template <typename T>
+        class ArenaAllocT {
+        public:
+            using value_type = T;
+            /** copy assignment: leave lhs allocator in place **/
+            using propagate_on_container_copy_assignment = std::false_type;
+            /** move assignment: adopt rhs allocator
+             *  (Forced: cannot mix allocations from different allocators
+             *  within a container)
+             **/
+            using propagate_on_container_move_assignment = std::true_type;
+            /** swap: also swap allocators
+             *  (Forced: cannot mix allocations from different allocators
+             *  within a containers)
+             **/
+            using propagate_on_container_swap = std::true_type;
+            /** An ArenaAlloc instance is unique owner of its own memory:
+             *  no other instance can dealloc
+             **/
+            using is_always_equal = std::false_type;
+
+        public:
+            explicit ArenaAllocT(ArenaAlloc * mm) : mm_{mm} {}
+            ArenaAllocT(const ArenaAllocT & other) = default;
+
+            /** rebind ctor. Allows container to use supplied allocator
+             *  for multiple types
+             **/
+            template <typename U>
+            ArenaAllocT(const ArenaAllocT<U> & other) noexcept : mm_{other.mm_} {}
+
+            T * allocate(size_t n) {
+                void * mem = mm_->alloc(n * sizeof(T));
+
+                return reinterpret_cast<T *>(mem);
+            }
+
+            void deallocate(T * p, size_t n) noexcept {
+                assert(mm_->contains(p));
+                assert(n == 0 || mm_->contains(p + n - 1));
+
+                //arena_->deallocate(p, n * sizeof(T));
+            }
+
+            bool operator==(const ArenaAllocT & other) const {
+                return mm_ == other.mm_;
+            }
+
+            bool operator!=(const ArenaAllocT & other) const {
+                return mm_ != other.mm_;
+            }
+
+            ArenaAlloc * mm_ = nullptr;
+        };
+    } /*namespace gc*/
+} /*namespace xo*/
+
+/* end Allocator.hpp */

utest/ArenaAllocT.test.cpp

@@ -0,0 +1,65 @@
+/** @file ArenaAllocT.test.cpp
+ *
+ *  @author Roland Conybeare, Nov 2025
+ **/
+
+#include "xo/alloc/ArenaAllocT.hpp"
+#include <catch2/catch.hpp>
+#include <map>
+
+namespace xo {
+    using xo::gc::ArenaAllocT;
+    using xo::gc::ArenaAlloc;
+
+    namespace ut {
+
+        namespace {
+            struct testcase_ArenaAllocT {
+                testcase_ArenaAllocT(std::size_t z) : arena_z_{z} {}
+
+                std::size_t arena_z_;
+                std::vector<std::pair<std::string, std::string>> kv_pairs_;
+            };
+
+            std::vector<testcase_ArenaAllocT>
+            s_testcase_v = {
+                testcase_ArenaAllocT(4096)
+            };
+        }
+
+        TEST_CASE("ArenaAllocT", "[alloc][traits]")
+        {
+            for (std::size_t i_tc = 0, n_tc = s_testcase_v.size(); i_tc < n_tc; ++i_tc) {
+                const testcase_ArenaAllocT & tc = s_testcase_v[i_tc];
+
+                constexpr bool c_debug_flag = true;
+
+                auto arena = ArenaAlloc::make("arena", tc.arena_z_, c_debug_flag);
+                auto alloc = ArenaAllocT<std::pair<const std::string, std::string>>(arena.get());
+
+                using TestMapType = std::map<std::string,
+                                             std::string,
+                                             std::less<std::string>,
+                                             ArenaAllocT<std::pair<const std::string, std::string>>>;
+
+                TestMapType test_map(alloc);
+
+                size_t n = 0;
+                for (const auto & kv_ix : tc.kv_pairs_) {
+                    test_map[kv_ix.first] = kv_ix.second;
+                    ++n;
+
+                    REQUIRE(test_map.size() == n);
+
+                    for (const auto & map_ix : test_map) {
+                        map_ix.first;
+                        map_ix.second;
+                    }
+                }
+
+            }
+        }
+    }
+} /*namespace xo*/
+
+/* end ArenaAllocT.test.cpp */

utest/CMakeLists.txt

@@ -7,6 +7,7 @@ set(UTEST_SRCS
     alloc_utest_main.cpp
     IAlloc.test.cpp
     ArenaAlloc.test.cpp
+    ArenaAllocT.test.cpp
     ListAlloc.test.cpp
     GC.test.cpp
     GcStatistics.test.cpp