How do you return multiple values and assign them to mutable variables?

F# has "by reference" parameters just like C#, so you can write a classic swap function similarly:

let swap (x: byref<'a>) (y: byref<'a>) =
    let temp = x
    x <- y
    y <- temp

let mutable x,y = 1,2
swap &x &y

You can't; there's no syntax to update 'more than one mutable variable' with a single assignment. Of course you can do

let newX, newY = Swap(x,y)
x <- newX
y <- newY