From 01de5d42afdaae5348a2ca2e9f47bdf038d29b11 Mon Sep 17 00:00:00 2001
From: vadim-xd <vadim-xd@yandex-team.com>
Date: Tue, 19 May 2026 10:43:11 +0300
Subject: Add Concat for arbitrary string types
 commit_hash:b9f1c87173a18fb59f8cf684191efd4436dd6012

---
 library/cpp/containers/cow_string/cow_string.h | 40 +++-----------------------
 1 file changed, 4 insertions(+), 36 deletions(-)

(limited to 'library/cpp')

diff --git a/library/cpp/containers/cow_string/cow_string.h b/library/cpp/containers/cow_string/cow_string.h
index 0ffea0ac2bf..34dcff81e8a 100644
--- a/library/cpp/containers/cow_string/cow_string.h
+++ b/library/cpp/containers/cow_string/cow_string.h
@@ -321,44 +321,12 @@ public:
     }
 
 private:
-    template <typename T>
-    using TJoinParam = std::conditional_t<std::is_same_v<T, TCharType>, TCharType, TBasicStringBuf<TCharType, TTraits>>;
-
-    template <typename... R>
-    static size_t SumLength(const TBasicStringBuf<TCharType, TTraits> s1, const R&... r) noexcept {
-        return s1.size() + SumLength(r...);
-    }
-
-    template <typename... R>
-    static size_t SumLength(const TCharType /*s1*/, const R&... r) noexcept {
-        return 1 + SumLength(r...);
-    }
-
-    static constexpr size_t SumLength() noexcept {
-        return 0;
-    }
-
-    template <typename... R>
-    static void CopyAll(TCharType* p, const TBasicStringBuf<TCharType, TTraits> s, const R&... r) {
-        TTraits::copy(p, s.data(), s.size());
-        CopyAll(p + s.size(), r...);
-    }
-
-    template <typename... R, class TNextCharType, typename = std::enable_if_t<std::is_same<TCharType, TNextCharType>::value>>
-    static void CopyAll(TCharType* p, const TNextCharType s, const R&... r) {
-        p[0] = s;
-        CopyAll(p + 1, r...);
-    }
-
-    static void CopyAll(TCharType*) noexcept {
-    }
+    using TJoinHelper = TStringJoinHelper<TCharType, TTraits>;
 
     template <typename... R>
     static inline TBasicCowString JoinImpl(const R&... r) {
-        TBasicCowString s{TUninitialized{SumLength(r...)}};
-
-        TBasicCowString::CopyAll((TCharType*)s.data(), r...);
-
+        TBasicCowString s{TUninitialized{TJoinHelper::SumLength(r...)}};
+        TJoinHelper::CopyAll((TCharType*)s.data(), r...);
         return s;
     }
 
@@ -375,7 +343,7 @@ public:
 
     template <typename... R>
     static inline TBasicCowString Join(const R&... r) {
-        return JoinImpl(TJoinParam<R>(r)...);
+        return JoinImpl(typename TJoinHelper::template TJoinParam<R>(r)...);
     }
 
     // ~~~ Assignment ~~~ : FAMILY0(TBasicCowString&, assign);
-- 
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