movable TStringStream

Do not copy the internal string buffer in  move constructors and the move assignment operator.
19e6948ae4706272838bc76831b9ff2051a20590

2 files changed, 68 insertions, 2 deletions

diff --git a/util/stream/str.h b/util/stream/str.h
index 028bd572c0..1316dba800 100644
--- a/util/stream/str.h
+++ b/util/stream/str.h
@@ -125,6 +125,13 @@ public:
     {
     }
 
+    inline TStringStream(TString&& string)
+        : TEmbeddedString(std::move(string))
+        , TStringInput(*TEmbeddedString::Ptr())
+        , TStringOutput(*TEmbeddedString::Ptr())
+    {
+    }
+
     inline TStringStream(const TStringStream& other)
         : TEmbeddedString(other.Str())
         , TStringInput(*TEmbeddedString::Ptr())
@@ -132,6 +139,14 @@ public:
     {
     }
 
+    inline TStringStream(TStringStream&& other)
+        : TEmbeddedString(std::move(other).Str())
+        , TStringInput(*TEmbeddedString::Ptr())
+        , TStringOutput(*TEmbeddedString::Ptr())
+    {
+        other.Pos_ = 0;
+    }
+
     inline TStringStream& operator=(const TStringStream& other) {
         // All references remain alive, we need to change position only
         Str() = other.Str();
@@ -140,6 +155,15 @@ public:
         return *this;
     }
 
+    inline TStringStream& operator=(TStringStream&& other) {
+        // All references remain alive, we need to change position only
+        Str() = std::move(other).Str();
+        Pos_ = other.Pos_;
+        other.Pos_ = 0;
+
+        return *this;
+    }
+
     ~TStringStream() override;
 
     /**
@@ -152,18 +176,25 @@ public:
     /**
      * @returns                         String that this stream is writing into.
      */
-    inline TString& Str() noexcept {
+    inline TString& Str() & noexcept {
         return *Ptr();
     }
 
     /**
      * @returns                         String that this stream is writing into.
      */
-    inline const TString& Str() const noexcept {
+    inline const TString& Str() const& noexcept {
         return *Ptr();
     }
 
     /**
+     * @returns                         String that this stream is writing into.
+     */
+    inline TString&& Str() && noexcept {
+        return std::move(*Ptr());
+    }
+
+    /**
      * @returns                         Pointer to the character data contained
      *                                  in this stream. The data is guaranteed
      *                                  to be null-terminated.
diff --git a/util/stream/str_ut.cpp b/util/stream/str_ut.cpp
index 534b58d71c..c5ab9ca5e9 100644
--- a/util/stream/str_ut.cpp
+++ b/util/stream/str_ut.cpp
@@ -2,6 +2,7 @@
 
 #include <library/cpp/testing/unittest/registar.h>
 #include <util/generic/typetraits.h>
+#include <util/string/join.h>
 
 template <typename T>
 const T ReturnConstTemp();
@@ -150,6 +151,40 @@ Y_UNIT_TEST_SUITE(TStringInputOutputTest) {
         output1 << "baz";
     }
 
+    Y_UNIT_TEST(MoveableStringInputStream) {
+        TString data{JoinSeq("\n", "qwertyuiop"sv)};
+        TStringInput in0{data};
+        TString str;
+        in0 >> str;
+        UNIT_ASSERT_VALUES_EQUAL(str, ToString(int('q')));
+        TStringInput in1{std::move(in0)};
+        in1 >> str;
+        UNIT_ASSERT_VALUES_EQUAL(str, ToString(int('w')));
+
+        // Check old stream is in a valid state
+        in0 >> str;
+    }
+
+    Y_UNIT_TEST(MoveableStringStream) {
+        TString str;
+        str.reserve(500);
+        const char* ptr = str.data();
+        TStringStream stream{std::move(str)};
+        stream << "foo"
+               << "bar";
+        TString out = std::move(stream).Str();
+        UNIT_ASSERT_EQUAL(ptr, out.data());
+        UNIT_ASSERT_STRINGS_EQUAL(out, "foobar");
+
+        TStringStream multiline{JoinSeq("\n", "qwertyuiop"sv)};
+        multiline >> str;
+        UNIT_ASSERT_VALUES_EQUAL(str, ToString(int('q')));
+        TStringStream other = std::move(multiline);
+        // Check old stream is in a valid state
+        multiline >> str;
+        multiline << "bar";
+    }
+
     // There is no distinct tests for Out<> via IOutputStream.
     // Let's tests strings output here.
     Y_UNIT_TEST(TestWritingWideStrings) {