fix uvalue deref traits

ref: https://github.com/BlackMATov/meta.hpp/issues/100

develop/untests/meta_utilities/value_tests.cpp

@@ -107,11 +107,17 @@ namespace
     bool operator==(const ivec2_big& l, const ivec2_big& r) noexcept {
         return l.x == r.x && l.y == r.y;
     }
+
+    struct deref_custom_class {
+        int operator*() const { return 42; }
+    };
 }
 
 META_HPP_DECLARE_COPY_TRAITS_FOR(ivec2)
 META_HPP_DECLARE_COPY_TRAITS_FOR(ivec2_big)
 
+META_HPP_DECLARE_DEREF_TRAITS_FOR(deref_custom_class)
+
 TEST_CASE("meta/meta_utilities/value/_") {
     namespace meta = meta_hpp;
 
@@ -645,6 +651,18 @@ TEST_CASE("meta/meta_utilities/value") {
             meta::uvalue v{std::make_unique<int>(42)};
             CHECK((*v).as<int>() == 42);
         }
+        {
+            CHECK(meta::uvalue{std::make_shared<std::vector<std::shared_ptr<int>>>()}.has_deref_op());
+            CHECK_FALSE(meta::uvalue{std::make_shared<std::vector<std::unique_ptr<int>>>()}.has_deref_op());
+        }
+        {
+            const meta::uvalue v{deref_custom_class{}};
+            CHECK(v.has_deref_op());
+
+            const meta::uvalue u = *v;
+            CHECK(u.get_type() == meta::resolve_type<int>());
+            CHECK(u.as<int>() == 42);
+        }
     }
 
     SUBCASE("less/equal") {

headers/meta.hpp/meta_detail/value_traits/deref_traits.hpp

@@ -9,6 +9,8 @@
 #include "../../meta_base.hpp"
 #include "../../meta_uvalue.hpp"
 
+#include "copy_traits.hpp"
+
 namespace meta_hpp::detail
 {
     template < typename T >
@@ -22,7 +24,7 @@ namespace meta_hpp::detail
 namespace meta_hpp::detail
 {
     template < typename T >
-        requires std::is_copy_constructible_v<T>
+        requires has_copy_traits<T>
     struct deref_traits<T*> {
         uvalue operator()(T* v) const {
             return v != nullptr ? uvalue{*v} : uvalue{};
@@ -30,18 +32,33 @@ namespace meta_hpp::detail
     };
 
     template < typename T >
-        requires std::is_copy_constructible_v<T>
+        requires has_copy_traits<T>
     struct deref_traits<std::shared_ptr<T>> {
-        uvalue operator()(const std::shared_ptr<T>& v) const {
+        using value_t = std::shared_ptr<T>;
+
+        uvalue operator()(const value_t& v) const {
             return v != nullptr ? uvalue{*v} : uvalue{};
         }
     };
 
     template < typename T, typename Deleter >
-        requires std::is_copy_constructible_v<T>
+        requires has_copy_traits<T>
     struct deref_traits<std::unique_ptr<T, Deleter>> {
-        uvalue operator()(const std::unique_ptr<T, Deleter>& v) const {
+        using value_t = std::unique_ptr<T, Deleter>;
+
+        uvalue operator()(const value_t& v) const {
             return v != nullptr ? uvalue{*v} : uvalue{};
         }
     };
 }
+
+#define META_HPP_DECLARE_DEREF_TRAITS_FOR(T) \
+    namespace meta_hpp::detail \
+    { \
+        template <> \
+        struct deref_traits<T> { \
+            uvalue operator()(const T& v) const { \
+                return uvalue{*v}; \
+            } \
+        }; \
+    }