feat: Add policy

Author: FrozenLemonTee

src/traits/policy.cppm

@@ -0,0 +1,81 @@
+module;
+#include <type_traits>
+
+export module mcpplibs.primitive.traits.policy;
+
+export namespace mcpplibs::primitive {
+
+namespace policy {
+
+enum class category { value, type, error, concurrency };
+
+template <typename P> struct traits {
+  static constexpr bool enabled = false;
+  static constexpr category kind = static_cast<category>(-1);
+};
+
+struct checked_value {};
+struct unchecked_value {};
+
+struct strict_type {};
+struct relaxed_type {};
+
+struct throw_error {};
+struct expected_error {};
+
+struct single_thread {};
+struct atomic {};
+
+template <> struct traits<checked_value> {
+  static constexpr bool enabled = true;
+  static constexpr category kind = category::value;
+};
+
+template <> struct traits<unchecked_value> {
+  static constexpr bool enabled = true;
+  static constexpr category kind = category::value;
+};
+
+template <> struct traits<strict_type> {
+  static constexpr bool enabled = true;
+  static constexpr category kind = category::type;
+};
+
+template <> struct traits<relaxed_type> {
+  static constexpr bool enabled = true;
+  static constexpr category kind = category::type;
+};
+
+template <> struct traits<throw_error> {
+  static constexpr bool enabled = true;
+  static constexpr category kind = category::error;
+};
+
+template <> struct traits<expected_error> {
+  static constexpr bool enabled = true;
+  static constexpr category kind = category::error;
+};
+
+template <> struct traits<single_thread> {
+  static constexpr bool enabled = true;
+  static constexpr category kind = category::concurrency;
+};
+
+template <> struct traits<atomic> {
+  static constexpr bool enabled = true;
+  static constexpr category kind = category::concurrency;
+};
+
+template <typename P>
+concept policy_type = traits<P>::enabled;
+
+struct default_policies {
+  using value = unchecked_value;
+  using type = relaxed_type;
+  using error = throw_error;
+  using concurrency = single_thread;
+};
+
+} // namespace policy
+
+} // namespace mcpplibs::primitive

src/traits/traits.cppm

@@ -3,3 +3,4 @@ module;
 export module mcpplibs.primitive.traits;
 
 export import mcpplibs.primitive.traits.underlying;
+export import mcpplibs.primitive.traits.policy;