structuomunmanaged.fs

// Author: Zoltan Podlovics
// License: Apache License, Version 2.0, https://www.apache.org/licenses/
// Description: Proof of concept demo of FSharp on struct field UOM. 
// After commenting source of compilation error in the main,
// "let (s2: S2) = readPtr ptr" 
// the generated bytecode show no differences between the S1 and S2 struct
// representation the uom type easure works as expected.
// 
// Usage:
//   fsharpc structuomunmanaged.fs
//
// Error message:
//   FS0001: A generic construct requires that the type 'S2' is an unmanaged type

#nowarn "9"

open System.Runtime.InteropServices
open Microsoft.FSharp.NativeInterop

[<Measure>]
type Version

[<NoComparison;NoEquality>]
[<Struct>]
type S1 =
  val i: int64
  val v: int64

[<NoComparison;NoEquality>]
[<Struct>]
type S2 =
  val i: int64
  val v: int64<Version>

[<Unverifiable>]
let readPtr (b: nativeptr<byte>): 'T when 'T: unmanaged and 'T: struct =
  let iPtr = NativePtr.toNativeInt b in
  let tPtr = NativePtr.ofNativeInt<'T> iPtr in
  NativePtr.read tPtr


[<EntryPoint>] 
let main (args : string[]) =
 let (buffer: byte array) = Array.zeroCreate 64
 let handle = GCHandle.Alloc(buffer, GCHandleType.Pinned) in
 let ptr = handle.AddrOfPinnedObject() |> NativePtr.ofNativeInt<byte>
 
 let (s1: S1) = readPtr ptr
 let (s2: S2) = readPtr ptr

 //return
 0