Question

Does it imply that whenever I am passed an array of a non nullable type, I should still check if it is null? Actually it is not even possible to check <> null but have to use operator.unchecked .How is it better than C#?

type test=
    {
        value: int
    }

let solution = Array.zeroCreate 10

solution.[0] <- {value = 1}
solution.[1].value   // System.NullReferenceException: Object reference not set to an instance of an object

type test =
  {value: int;}
val solution : test [] =
  [|{value = 1;}; null; null; null; null; null; null; null; null; null|]
val it : unit = ()

Answer 1

It depends where the array is being passed from.

If the array is created and used only within F#, then no, you don’t need to check for null; in fact, you shouldn’t check for null (using Unchecked.defaultOf) because the F# compiler optimizes some special values like [] (and None, in certain cases) by representing them as null in the compiled IL.

If you’re consuming an array being passed in by code written in another language (such as C#), then yes, you should still check for null. If the calling code just creates the array and doesn’t mutate it any further, then you’ll only need to perform the null checks once.

EDIT : Here’s a previous discussion about how the F# compiler optimizes the representation of certain values using null: Why is None represented as null?