G-API utils - fix compilation error in variant::operator=

modules/gapi/include/opencv2/gapi/util/variant.hpp

@@ -281,13 +281,14 @@ namespace util
     template<class T> typename detail::are_different<variant<Ts...>, T, variant<Ts...>&>
     ::type variant<Ts...>::operator=(T&& t) noexcept
     {
+        using decayed_t = typename std::decay<T>::type;
         // FIXME: No version with implicit type conversion available!
         static const constexpr std::size_t t_index =
-            util::type_list_index<T, Ts...>::value;
+            util::type_list_index<decayed_t, Ts...>::value;
 
         if (t_index == m_index)
         {
-            util::get<T>(*this) = std::move(t);
+            util::get<decayed_t>(*this) = std::move(t);
             return *this;
         }
         else return (*this = variant(std::move(t)));

modules/gapi/test/util/variant_tests.cpp

@@ -115,6 +115,18 @@ TEST(Variant, Assign_Basic)
     EXPECT_EQ(42, util::get<int>(vis));
 }
 
+TEST(Variant, Assign_LValueRef)
+{
+    TestVar vis;
+    EXPECT_EQ(0u, vis.index());
+    EXPECT_EQ(0,  util::get<int>(vis));
+
+    int val = 42;
+    vis = val;
+    EXPECT_EQ(0u, vis.index());
+    EXPECT_EQ(42, util::get<int>(vis));
+}
+
 TEST(Variant, Assign_ValueUpdate_SameType)
 {
     TestVar vis(42);
@@ -139,6 +151,19 @@ TEST(Variant, Assign_ValueUpdate_DiffType)
     EXPECT_EQ("42", util::get<std::string>(vis));
 }
 
+TEST(Variant, Assign_LValueRef_DiffType)
+{
+    TestVar vis(42);
+
+    EXPECT_EQ(0u, vis.index());
+    EXPECT_EQ(42, util::get<int>(vis));
+
+    std::string s("42");
+    vis = s;
+    EXPECT_EQ(1u, vis.index());
+    EXPECT_EQ("42", util::get<std::string>(vis));
+}
+
 TEST(Variant, Assign_ValueUpdate_Const)
 {
     TestVar va(42);