Question

Assume the following code:

let fn () =
  use a = new System.IO.StreamWriter ("d:\\test.txt")
  a

let b = fn ()
b.Write "t"

It gives following error:

ObjectDisposedException: Cannot write to a closed TextWriter.

Why is that?

Answer 1

use is scoped to the function fn so when a is returned it also disposed.

The easiest way to cure this is:

let fn () =
  let a = new System.IO.StreamWriter ("d:\\test.txt")
  a

let main() = 
  use b = fn ()
  b.Write "t"
main()