# Method Stdio.Buffer()->__fd_set_output()

Method __fd_set_output

  `int __fd_set_output(object|function(string:int) write_callback)`

Description

  This tells the buffer to trigger the write callback for the specified filedescriptor when data is added to the buffer.

  This is used internally by Stdio.File to handle nonblocking buffered mode, and is not really intended to be used directly.

  If write_callback is `0` (zero) the state is cleared.