How to convert out/ref extern parameters to F#

I've got a C# extern declaration that goes like this:

    [DllImport("something.dll")]
    public static extern ReturnCode GetParent(IntPtr inRef, out IntPtr outParentRef);

How to开发者_开发技巧 translate that to F#?

You can try something like the code below. I don't know what ReturnCode is, so the code below expects it is an integer. For any more complex type, you'll need to use [<Struct>] attribute as in the answer referenced by A-Dubb.

type ReturnCode = int

[<System.Runtime.InteropServices.DllImport("something.dll")>]
extern ReturnCode GetParent(System.IntPtr inRef, System.IntPtr& outParentRef);

To call the function, you'd write something like this:

let mutable v = nativeint 10
let n = GetParent(nativeint 0, &v)

BTW: Could you also post a sample C code that implements the function in something.dll? If yes, we could try running the solution before sending an answer...

Maybe this similar question will point you in the right direction. Looks like he used attributes at the parameter level for "in" and "out" F# syntax for P/Invoke signature using MarshalAs

For anyone else trying to use F# with EnvDte via PInvoke this may help:

[<System.Runtime.InteropServices.DllImport("ole32.dll")>] 
extern unit CreateBindCtx(System.IntPtr inRef, IBindCtx& outParentRef);
[<System.Runtime.InteropServices.DllImport("ole32.dll")>]
extern unit GetRunningObjectTable(System.IntPtr inRef, IRunningObjectTable& outParentRef);

which apparently is slightly incorrect, but appears to work. the definition should be:

[<System.Runtime.InteropServices.DllImport("ole32.dll")>] 
extern int CreateBindCtx(System.IntPtr inRef, IBindCtx& outParentRef);
[<System.Runtime.InteropServices.DllImport("ole32.dll")>]
extern int GetRunningObjectTable(System.IntPtr inRef, IRunningObjectTable& outParentRef);