Samples from Matt Ellis "Writing Allocation Free Code in C#" talk

byref.samples.fs

// replicating same techniques as
// https://youtu.be/1ZJ8ROVS5gk?t=1435

[<Struct>]
type Point =
    val mutable X : int
    val mutable Y : int
    new(x, y) = { X = x; Y = y }

type Enemy(location: Point) =
  let mutable location = location
  member x.GetLocation() = location
  member x.GetLocationRef() = &location

let areEqual x y =
  if x = y then () else failwithf "not equal"

let ``struct return value is a copy`` () =
  let enemy = Enemy(Point(10,10))
  let mutable location = enemy.GetLocation()
  location.X <- 12
  areEqual 12 location.X
  areEqual 10 (enemy.GetLocation().X)

let ``ref return value is a copy`` () =
  let enemy = Enemy(Point(10,10))
  let mutable point = enemy.GetLocationRef()
  point.X <- 12
  areEqual 12 point.X
  areEqual 10 (enemy.GetLocation().X)

let ``ref return to ref not a copy`` () =
  let enemy = Enemy(Point(10,10))
  let point = &enemy.GetLocationRef()
  point.X <- 12
  areEqual 12 point.X
  areEqual 12 (enemy.GetLocation().X)

let ``method as lhs`` () =
  let enemy = Enemy(Point(10,10))
  enemy.GetLocationRef() <- Point(42,42)
  areEqual 42 (enemy.GetLocation().X)