F# Option equivalent of C#'s ?? operator

Question

I am looking for a way to get the value of an F# option or use a default value if it is None. This seems so common I can\'t believe something predefined doesn\'t exist. Here

Answer 1

You're looking for defaultArg [MSDN] ('T option -> 'T -> 'T).

It's often used to provide a default value for optional arguments:

type T(?arg) =
  member val Arg = defaultArg arg 0

let t1 = T(1) 
let t2 = T() //t2.Arg is 0