1 files changed, 116 insertions, 0 deletions
diff --git a/library/cpp/yt/string/string_builder.h b/library/cpp/yt/string/string_builder.h
new file mode 100644
index 0000000000..0e13e70904
--- /dev/null
+++ b/library/cpp/yt/string/string_builder.h
@@ -0,0 +1,116 @@
+#pragma once
+
+#include <util/generic/string.h>
+
+namespace NYT {
+
+////////////////////////////////////////////////////////////////////////////////
+
+// Forward declarations.
+class TStringBuilderBase;
+class TStringBuilder;
+class TDelimitedStringBuilderWrapper;
+
+template <size_t Length, class... TArgs>
+void Format(TStringBuilderBase* builder, const char (&format)[Length], TArgs&&... args);
+template <class... TArgs>
+void Format(TStringBuilderBase* builder, TStringBuf format, TArgs&&... args);
+
+////////////////////////////////////////////////////////////////////////////////
+
+//! A simple helper for constructing strings by a sequence of appends.
+class TStringBuilderBase
+{
+public:
+    virtual ~TStringBuilderBase() = default;
+
+    char* Preallocate(size_t size);
+
+    size_t GetLength() const;
+
+    TStringBuf GetBuffer() const;
+
+    void Advance(size_t size);
+
+    void AppendChar(char ch);
+    void AppendChar(char ch, int n);
+
+    void AppendString(TStringBuf str);
+    void AppendString(const char* str);
+
+    template <size_t Length, class... TArgs>
+    void AppendFormat(const char (&format)[Length], TArgs&&... args);
+    template <class... TArgs>
+    void AppendFormat(TStringBuf format, TArgs&&... args);
+
+    void Reset();
+
+protected:
+    char* Begin_ = nullptr;
+    char* Current_ = nullptr;
+    char* End_ = nullptr;
+
+    virtual void DoReset() = 0;
+    virtual void DoPreallocate(size_t newLength) = 0;
+
+    // -64 must account for any reasonable overhead in dynamic string allocation.
+    static constexpr size_t MinBufferLength = 1024 - 64;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+
+class TStringBuilder
+    : public TStringBuilderBase
+{
+public:
+    TString Flush();
+
+protected:
+    TString Buffer_;
+
+    void DoReset() override;
+    void DoPreallocate(size_t size) override;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+
+template <class T>
+TString ToStringViaBuilder(const T& value, TStringBuf spec = TStringBuf("v"));
+
+////////////////////////////////////////////////////////////////////////////////
+
+//! Appends a certain delimiter starting from the second call.
+class TDelimitedStringBuilderWrapper
+    : private TNonCopyable
+{
+public:
+    TDelimitedStringBuilderWrapper(
+        TStringBuilderBase* builder,
+        TStringBuf delimiter = TStringBuf(", "))
+        : Builder_(builder)
+        , Delimiter_(delimiter)
+    { }
+
+    TStringBuilderBase* operator->()
+    {
+        if (!FirstCall_) {
+            Builder_->AppendString(Delimiter_);
+        }
+        FirstCall_ = false;
+        return Builder_;
+    }
+
+private:
+    TStringBuilderBase* const Builder_;
+    const TStringBuf Delimiter_;
+
+    bool FirstCall_ = true;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+
+} // namespace NYT
+
+#define STRING_BUILDER_INL_H_
+#include "string_builder-inl.h"
+#undef STRING_BUILDER_INL_H_