faster implicit `TString` → `const std::string&` conversion: using template operator TStringType& to deprioritize non-const method

Converting a `TString` to a `const std::string&` should not cause data cloning.
commit_hash:df425bd56f8517d882444e15f3cc586af92d90b3

2 files changed, 14 insertions, 1 deletions

diff --git a/util/generic/string.h b/util/generic/string.h
index bbe340781a..3476f71b68 100644
--- a/util/generic/string.h
+++ b/util/generic/string.h
@@ -861,7 +861,8 @@ public:
         return this->ConstRef();
     }
 
-    operator TStringType&() & {
+    template <typename T, typename = std::enable_if_t<std::is_same_v<T, TStringType>>>
+    operator T&() & {
         return this->MutRef();
     }
 
diff --git a/util/generic/string_ut.cpp b/util/generic/string_ut.cpp
index bfd86bb07e..01c7a01188 100644
--- a/util/generic/string_ut.cpp
+++ b/util/generic/string_ut.cpp
@@ -1243,4 +1243,16 @@ Y_UNIT_TEST_SUITE(Interop) {
     Y_UNIT_TEST(TestTemp) {
         UNIT_ASSERT_VALUES_EQUAL("x" + ConstRef(TString("y")), "xy");
     }
+
+    static void ComparePointers(const std::string& s, const void* expected, TStringBuf descr) {
+        UNIT_ASSERT_VALUES_EQUAL_C(static_cast<const void*>(s.c_str()), expected, descr);
+    }
+
+    Y_UNIT_TEST(TestConstShared) {
+        TString s(600, 'a');
+        const void* stringStart = s.c_str();
+        ComparePointers(s, stringStart, "unique");
+        TString shared{s};
+        ComparePointers(s, stringStart, "shared"); // converting a TString to a `const std::string&` should not cause data cloning
+    }
 } // Y_UNIT_TEST_SUITE(Interop)