+# Things that can be efficienlty writen to a OStream
+#
+# The point of this interface it to allow is instance to be efficenty
+# writen into a OStream without having to allocate a big String object
+#
+# ready-to-save documents usually provide this interface.
+interface Streamable
+ # Write itself to a `stream`
+ # The specific logic it let to the concrete subclasses
+ fun write_to(stream: OStream) is abstract
+
+ # Like `write_to` but return a new String (may be quite large)
+ #
+ # This funtionnality is anectodical, since the point
+ # of streamable object to to be efficienlty written to a
+ # stream without having to allocate and concatenate strings
+ fun write_to_string: String
+ do
+ var stream = new StringOStream
+ write_to(stream)
+ return stream.to_s
+ end
+end
+
+redef class Text
+ super Streamable
+ redef fun write_to(stream) do stream.write(self)
+end
+
+redef class RopeNode
+ super Streamable
+end
+
+redef class Leaf
+
+ redef fun write_to(s) do s.write(str)
+end
+
+redef class Concat
+
+ redef fun write_to(s)
+ do
+ if left != null then left.write_to(s)
+ if right != null then right.write_to(s)
+ end
+end
+
+redef class RopeString
+
+ redef fun write_to(s) do root.write_to(s)
+end
+