detect reference_wrapper by partial specialization

is_ref_wrap previously treated any type with a nested ::type as a wrapper. Specialize on std::reference_wrapper so traits like std::decay are excluded, and keep the check C++14-friendly.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: wang-bin

jmi.h

@@ -329,11 +329,10 @@ struct is_jarray_cpp : integral_constant<bool, (is_array_like<T>::value || is_ar
     && !is_same<typename decay<T>::type, char*>::value
     && !is_same<typename decay<T>::type, const char*>::value> {};
 
-template<class T, typename = void>
-struct is_ref_wrap :false_type{};
-
 template<class T>
-struct is_ref_wrap<T, decltype(void(!declval<is_same<reference_wrapper<typename T::type>, remove_cvref_t<T>>>()))>: true_type{};
+struct is_ref_wrap : false_type {};
+template<class T>
+struct is_ref_wrap<reference_wrapper<T>> : true_type {};
 
 template<typename T>
 using if_jarray_cpp = typename enable_if<is_jarray_cpp<T>::value, bool>::type;

test/signature.cpp

@@ -25,6 +25,8 @@ constexpr bool CstrEq(const array<char, N>& a, const char* b) {
 static_assert(CstrEq(jmi::signature_of<jobject>(), "Ljava/lang/Object;"), "");
 static_assert(CstrEq(jmi::signature_of<jstring>(), "Ljava/lang/String;"), "");
 static_assert(CstrEq(jmi::signature_of<jintArray>(), "[I"), "");
+static_assert(jmi::detail::is_ref_wrap<reference_wrapper<int>>::value, "");
+static_assert(!jmi::detail::is_ref_wrap<decay<int>>::value, "");
 extern "C" jint JNICALL JNI_OnLoad(JavaVM* vm, void*)
 {
     JNIEnv* env = nullptr;