[From VSTS] Getting ref to static mutable field is an error in F# 4.5

Referencing a class static mutable field via & stopped compiling in F# 4.5. Example:

```fsharp
type MyClass () =
[]
static val mutable private nextInstanceIndex : int
static do
MyClass.nextInstanceIndex <- 1
let instanceIndex = System.Threading.Interlocked.Increment(&MyClass.nextInstanceIndex) - 1
```

Compilation results in error FS3236: Cannot take the address of the value returned from the expression. Assign the returned value to a let-bound value before taking the address.

_This issue has been moved from https://developercommunity.visualstudio.com/content/problem/301281/getting-ref-to-static-mutable-field-is-an-error-in.html
VSTS ticketId: 655347_
_These are the original issue comments:_

James Horvath on 7/27/2018, 08:32 AM (3 days ago):

Here's that code formatted:

type MyClass () =

	[<DefaultValue>]

	static val mutable private nextInstanceIndex : int

	static do

		MyClass.nextInstanceIndex <- 1

	let instanceIndex = System.Threading.Interlocked.Increment(&MyClass.nextInstanceIndex) - 1

_These are the original issue solutions:_
(no solutions)