Make persist compatible with C++17

doc/persist-introduction.rst

@@ -15,7 +15,7 @@ Dependencies
 ------------
 
 In addition to the `dependencies <introduction.html#dependencies>`_ of
-``immer``, this library makes use of **C++20**, `Boost.Hana
+``immer``, this library makes use of **C++17**, `Boost.Hana
 <https://boostorg.github.io/hana/>`_, `fmt <https://fmt.dev/>`_ and
 `cereal <https://uscilab.github.io/cereal/>`_.
 

extra/fuzzer/persist/CMakeLists.txt

@@ -6,6 +6,8 @@ foreach(_file IN LISTS immer_fuzzers)
   add_executable(${_target} EXCLUDE_FROM_ALL "${_file}")
   set_target_properties(${_target} PROPERTIES OUTPUT_NAME ${_output})
   target_compile_options(${_target} PUBLIC ${immer_fuzzing_engine})
+  target_compile_options(${_target} PRIVATE ${immer_fuzzing_engine}
+                                            -Wno-c++20-designator)
   target_include_directories(${_target} PRIVATE ../..)
   target_link_libraries(${_target} PUBLIC ${immer_fuzzing_engine} immer-dev)
   add_dependencies(fuzzers ${_target})

extra/fuzzer/persist/flex-vector.cpp

@@ -18,7 +18,8 @@
 #include <array>
 
 namespace {
-void require_eq(const auto& a, const auto& b)
+template <class T>
+void require_eq(const T& a, const T& b)
 {
     if (a != b) {
         throw std::runtime_error{

flake.nix

@@ -200,7 +200,7 @@
             "-Dimmer_BUILD_TESTS=ON"
             "-Dimmer_BUILD_PERSIST_TESTS=ON"
             "-Dimmer_BUILD_EXAMPLES=OFF"
-            "-DCXX_STANDARD=20"
+            "-DCXX_STANDARD=17"
           ];
         });
       };

immer/extra/persist/cereal/archives.hpp

@@ -60,7 +60,10 @@ struct blackhole_output_archive
 // blackhole_output_archive doesn't care about names
 struct empty_name_fn
 {
-    void operator()(const auto& container) const {}
+    template <class T>
+    void operator()(const T& container) const
+    {
+    }
 };
 
 template <class Pools>
@@ -99,15 +102,13 @@ class output_pools_cereal_archive_wrapper
 
     template <class... Args>
     explicit output_pools_cereal_archive_wrapper(Args&&... args)
-        requires std::is_same_v<WrapFn, boost::hana::id_t>
         : cereal::OutputArchive<output_pools_cereal_archive_wrapper>{this}
         , previous{std::forward<Args>(args)...}
     {
     }
 
     template <class... Args>
     output_pools_cereal_archive_wrapper(Pools pools_, Args&&... args)
-        requires std::is_same_v<WrapFn, boost::hana::id_t>
         : cereal::OutputArchive<output_pools_cereal_archive_wrapper>{this}
         , previous{std::forward<Args>(args)...}
         , pools{std::move(pools_)}
@@ -279,7 +280,6 @@ class input_pools_cereal_archive_wrapper
 
     template <class... Args>
     input_pools_cereal_archive_wrapper(Pools pools_, Args&&... args)
-        requires std::is_same_v<WrapFn, boost::hana::id_t>
         : cereal::InputArchive<input_pools_cereal_archive_wrapper>{this}
         , previous{std::forward<Args>(args)...}
         , pools{std::move(pools_)}

immer/extra/persist/cereal/load.hpp

@@ -15,8 +15,8 @@ namespace immer::persist {
  * @ingroup persist-api
  */
 template <class T,
-          class Archive    = cereal::JSONInputArchive,
-          Policy<T> Policy = default_policy,
+          class Archive = cereal::JSONInputArchive,
+          class Policy  = default_policy,
           class... Args>
 T cereal_load_with_pools(std::istream& is,
                          const Policy& policy = Policy{},
@@ -26,10 +26,7 @@ T cereal_load_with_pools(std::istream& is,
         decltype(boost::hana::to_set(policy.get_pool_types(std::declval<T>())));
     using Pools = decltype(detail::generate_input_pools(TypesSet{}));
 
-    auto get_pool_name_fn = [](const auto& value) {
-        return Policy{}.get_pool_name(value);
-    };
-    using PoolNameFn = decltype(get_pool_name_fn);
+    using PoolNameFn = get_pool_name_fn_t<Policy>;
 
     const auto wrap =
         detail::wrap_known_types(TypesSet{}, detail::wrap_for_loading);
@@ -53,8 +50,8 @@ T cereal_load_with_pools(std::istream& is,
  * @ingroup persist-api
  */
 template <class T,
-          class Archive    = cereal::JSONInputArchive,
-          Policy<T> Policy = default_policy>
+          class Archive = cereal::JSONInputArchive,
+          class Policy  = default_policy>
 T cereal_load_with_pools(const std::string& input,
                          const Policy& policy = Policy{})
 {

immer/extra/persist/cereal/policy.hpp

@@ -9,24 +9,6 @@ namespace immer::persist {
  * @defgroup persist-policy
  */
 
-/**
- * @brief Policy is a type that describes certain aspects of serialization for
- * `immer::persist`.
- *      - How to call into the `cereal` archive to save and load the
- * user-provided value. Can be used to serealize the value inline (without the
- * `value0` node) by taking a dependency on <a
- * href="https://github.com/LowCostCustoms/cereal-inline">cereal-inline</a>, for
- * example.
- *      - Types of `immer` containers that will be serialized using pools. One
- * pool contains nodes of only one `immer` container type.
- *      - Names for each per-type pool.
- *
- * @ingroup persist-policy
- */
-template <class T, class Value>
-concept Policy =
-    requires(Value value, T policy) { policy.get_pool_types(value); };
-
 template <class T>
 auto get_pools_names(const T&)
 {
@@ -67,6 +49,20 @@ struct value0_serialize_t
     }
 };
 
+/**
+ * @brief Policy is a type that describes certain aspects of serialization for
+ * `immer::persist`.
+ *      - How to call into the `cereal` archive to save and load the
+ * user-provided value. Can be used to serealize the value inline (without the
+ * `value0` node) by taking a dependency on <a
+ * href="https://github.com/LowCostCustoms/cereal-inline">cereal-inline</a>, for
+ * example.
+ *      - Types of `immer` containers that will be serialized using pools. One
+ * pool contains nodes of only one `immer` container type.
+ *      - Names for each per-type pool.
+ *
+ * @ingroup persist-policy
+ */
 template <class T>
 struct via_get_pools_names_policy_t : value0_serialize_t
 {
@@ -100,9 +96,10 @@ struct via_get_pools_names_policy_t : value0_serialize_t
  *
  * @ingroup persist-policy
  */
-auto via_get_pools_names_policy(const auto& value)
+template <class T>
+auto via_get_pools_names_policy(const T& value)
 {
-    return via_get_pools_names_policy_t<std::decay_t<decltype(value)>>{};
+    return via_get_pools_names_policy_t<std::decay_t<T>>{};
 }
 
 /**
@@ -187,12 +184,22 @@ struct hana_struct_auto_member_name_policy_t : value0_serialize_t
  *
  * @ingroup persist-policy
  */
-auto hana_struct_auto_member_name_policy(const auto& value)
+template <class T>
+auto hana_struct_auto_member_name_policy(const T& value)
 {
-    return hana_struct_auto_member_name_policy_t<
-        std::decay_t<decltype(value)>>{};
+    return hana_struct_auto_member_name_policy_t<std::decay_t<T>>{};
 }
 
 using default_policy = via_get_pools_types_policy;
 
+template <class Policy>
+struct get_pool_name_fn_t
+{
+    template <class T>
+    auto operator()(const T& value) const
+    {
+        return Policy{}.get_pool_name(value);
+    }
+};
+
 } // namespace immer::persist

immer/extra/persist/cereal/save.hpp

@@ -20,7 +20,7 @@ namespace immer::persist {
  */
 template <class Archive = cereal::JSONOutputArchive,
           class T,
-          Policy<T> Policy = default_policy,
+          class Policy = default_policy,
           class... Args>
 void cereal_save_with_pools(std::ostream& os,
                             const T& value0,
@@ -31,14 +31,11 @@ void cereal_save_with_pools(std::ostream& os,
     auto pools       = detail::generate_output_pools(types);
     const auto wrap  = detail::wrap_known_types(types, detail::wrap_for_saving);
     using Pools      = std::decay_t<decltype(pools)>;
-    auto get_pool_name_fn = [](const auto& value) {
-        return Policy{}.get_pool_name(value);
-    };
-    auto ar = immer::persist::output_pools_cereal_archive_wrapper<
+    auto ar          = immer::persist::output_pools_cereal_archive_wrapper<
         Archive,
         Pools,
         decltype(wrap),
-        decltype(get_pool_name_fn)>{
+        get_pool_name_fn_t<Policy>>{
         pools, wrap, os, std::forward<Args>(args)...};
     policy.save(ar, value0);
     // Calling finalize explicitly, as it might throw on saving the pools,
@@ -56,14 +53,14 @@ void cereal_save_with_pools(std::ostream& os,
  */
 template <class Archive = cereal::JSONOutputArchive,
           class T,
-          Policy<T> Policy = default_policy,
+          class Policy = default_policy,
           class... Args>
 std::string cereal_save_with_pools(const T& value0,
                                    const Policy& policy = Policy{},
                                    Args&&... args)
 {
     auto os = std::ostringstream{};
-    cereal_save_with_pools<Archive>(
+    cereal_save_with_pools<Archive, T, Policy>(
         os, value0, policy, std::forward<Args>(args)...);
     return os.str();
 }

immer/extra/persist/detail/alias.hpp

@@ -18,8 +18,15 @@ struct type_alias
     {
     }
 
-    friend bool operator==(const type_alias& left,
-                           const type_alias& right) = default;
+    friend bool operator==(const type_alias& left, const type_alias& right)
+    {
+        return left.value == right.value;
+    }
+
+    friend bool operator!=(const type_alias& left, const type_alias& right)
+    {
+        return left.value != right.value;
+    }
 
     /**
      * This works only starting with fmt v10.

immer/extra/persist/detail/array/pool.hpp

@@ -22,6 +22,11 @@ struct output_pool
         return left.arrays == right.arrays;
     }
 
+    friend bool operator!=(const output_pool& left, const output_pool& right)
+    {
+        return left.arrays != right.arrays;
+    }
+
     template <class Archive>
     void save(Archive& ar) const
     {
@@ -78,8 +83,10 @@ struct input_pool
 {
     immer::vector<immer::array<T, MemoryPolicy>> arrays;
 
-    friend bool operator==(const input_pool& left,
-                           const input_pool& right) = default;
+    friend bool operator==(const input_pool& left, const input_pool& right)
+    {
+        return left.arrays == right.arrays;
+    }
 
     template <class Archive>
     void load(Archive& ar)
@@ -125,7 +132,6 @@ class loader
 {
 public:
     explicit loader(Pool pool)
-        requires std::is_same_v<TransformF, boost::hana::id_t>
         : pool_{std::move(pool)}
     {
     }

immer/extra/persist/detail/box/pool.hpp

@@ -26,6 +26,11 @@ struct output_pool
         return left.boxes == right.boxes;
     }
 
+    friend bool operator!=(const output_pool& left, const output_pool& right)
+    {
+        return left.boxes != right.boxes;
+    }
+
     template <class Archive>
     void save(Archive& ar) const
     {
@@ -64,8 +69,10 @@ struct input_pool
 {
     immer::vector<immer::box<T, MemoryPolicy>> boxes;
 
-    friend bool operator==(const input_pool& left,
-                           const input_pool& right) = default;
+    friend bool operator==(const input_pool& left, const input_pool& right)
+    {
+        return left.boxes == right.boxes;
+    }
 
     template <class Archive>
     void load(Archive& ar)
@@ -141,7 +148,6 @@ class loader
 {
 public:
     explicit loader(Pool pool)
-        requires std::is_same_v<TransformF, boost::hana::id_t>
         : pool_{std::move(pool)}
     {
     }

immer/extra/persist/detail/cereal/input_archive_util.hpp

@@ -5,8 +5,8 @@
 
 namespace immer::persist::detail {
 
-template <class Pools, class Archive, class PoolNameFn>
-auto load_pools(std::istream& is, const auto& wrap)
+template <class Pools, class Archive, class PoolNameFn, class WrapF>
+auto load_pools(std::istream& is, const WrapF& wrap)
 {
     const auto reload_pool =
         [wrap](std::istream& is, Pools pools, bool ignore_pool_exceptions) {

immer/extra/persist/detail/cereal/persistable.hpp

@@ -51,8 +51,15 @@ struct persistable
     {
     }
 
-    friend bool operator==(const persistable& left,
-                           const persistable& right) = default;
+    friend bool operator==(const persistable& left, const persistable& right)
+    {
+        return left.container == right.container;
+    }
+
+    friend bool operator!=(const persistable& left, const persistable& right)
+    {
+        return left.container != right.container;
+    }
 };
 
 template <class Previous,

immer/extra/persist/detail/cereal/pools.hpp

@@ -170,7 +170,6 @@ struct input_pool
     input_pool() = default;
 
     explicit input_pool(Pool pool_)
-        requires std::is_same_v<TransformF, boost::hana::id_t>
         : pool{std::move(pool_)}
     {
     }
@@ -201,6 +200,11 @@ struct input_pool
         return left.pool == right.pool;
     }
 
+    friend bool operator!=(const input_pool& left, const input_pool& right)
+    {
+        return left.pool != right.pool;
+    }
+
     void merge_previous(const input_pool& original)
     {
         pool.merge_previous(original.pool);
@@ -429,7 +433,8 @@ class input_pools
     }
 };
 
-inline auto generate_output_pools(auto types)
+template <class T>
+auto generate_output_pools(T types)
 {
     auto storage =
         hana::fold_left(types, hana::make_map(), [](auto map, auto type) {
@@ -444,7 +449,8 @@ inline auto generate_output_pools(auto types)
     return output_pools<Storage>{storage};
 }
 
-inline auto generate_input_pools(auto types)
+template <class T>
+auto generate_input_pools(T types)
 {
     auto storage =
         hana::fold_left(types, hana::make_map(), [](auto map, auto type) {