StructLayout limitation in F# Interactive?

Question

I noticed that if I define a struct with StructLayout.Sequential, like so:

open System.Runtime.InteropServices

[<StructLayout(LayoutKind.Sequential, Pack=1)>]
type SomeType =
 val mutable Field1: uint32
 val mutable Field2: uint32

This compiles and works fine in a real program, but FSI gives error error FS0193: internal error: Could not load type 'SomeType' from assembly 'FSI-ASSEMBLY, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' because field 'Field1' was not given an explicit offset.

Is this a bug or limitation of FSI? Is there a workaround?

Answer 1

Workaround (the error has a hint):

[<Struct;StructLayout(LayoutKind.Explicit)>]
type SomeType =
    [<FieldOffset(0)>]
    val mutable Field1: uint32
    [<FieldOffset(4)>]
    val mutable Field2: uint32