class output_channel :Creates an output channel writing into an?onclose:unit -> unit -> Pervasives.out_channel ->out_obj_channel
out_channel.
The method pos_out reflects the real position in the channel as
returned by Pervasives.pos_out. This works for both seekable and
non-seekable channels.
The method close_out also closes the underlying out_channel.
onclose : this function is called when the close_out method is
invoked, just after the underlying out_channel has been closed.