intermediate changes

ref:cde9a383711a11544ce7e107a78147fb96cc4029

1 files changed, 44 insertions, 0 deletions

diff --git a/util/stream/holder.h b/util/stream/holder.h
new file mode 100644
index 0000000000..c60a4e510c
--- /dev/null
+++ b/util/stream/holder.h
@@ -0,0 +1,44 @@
+#pragma once
+
+#include <util/generic/ptr.h>
+
+#include <utility>
+#include <type_traits>
+
+class IInputStream;
+class IOutputStream;
+
+namespace NPrivate {
+    template <class Stream, bool isInput = std::is_base_of<IInputStream, Stream>::value>
+    struct TStreamBase {
+        using TType = IInputStream;
+    };
+
+    template <class Stream>
+    struct TStreamBase<Stream, false> {
+        using TType = IOutputStream;
+    };
+
+}
+
+/**
+ * An ownership-gaining wrapper for proxy streams.
+ *
+ * Example usage:
+ * \code
+ * TCountingInput* input = new THoldingStream<TCountingInput>(new TStringInput(s));
+ * \encode
+ *
+ * In this example, resulting counting input also owns a string input that it
+ * was constructed on top of.
+ */
+template <class Base, class StreamBase = typename ::NPrivate::TStreamBase<Base>::TType>
+class THoldingStream: private THolder<StreamBase>, public Base {
+public:
+    template <class... Args>
+    inline THoldingStream(THolder<StreamBase> stream, Args&&... args)
+        : THolder<StreamBase>(std::move(stream))
+        , Base(this->Get(), std::forward<Args>(args)...)
+    {
+    }
+};