voidptr should be an unmanaged type

[krauthaufen]

Currently F# does not treat voidptr as an unmanaged type.
Therefore types like nativeptr<voidptr>, etc. cause compiler errors.

However on IL level this works and C# libraries (e.g. Silk.NET.OpenGL) expose methods expecting this kind of argument (which currently can't be created in F# due the above)

Expected behavior

voidptr should be treated as an unmanaged type

Known workarounds

Sadly I couldn't come up with a workaround. If anyone has an idea I would be glad to hear it!

Related information

Tested on VS2019 with .NET5 and FSharp.Core 5.0.0

[zpodlovics]

The base library pointer types (e.g.: System.Int32*) including System.Void* are not a value types. So it seems that void** functionality is not yet available (as of dotnet/runtime#44968)

> System.Type.GetType("System.Int32*").IsValueType;;
val it : bool = false

> System.Type.GetType("System.Void*").IsValueType;;
val it : bool = false

however System.IntPtr is:

> System.Type.GetType("System.IntPtr").IsValueType;;
val it : bool = true

[krauthaufen]

In F# nativeptr<int> is treated as an unmanaged type and i have a C# library here exposing a void** so this can't be entirely true...

[zpodlovics]

nativeptr is just s syntactic sugar around System.IntPtr (nativeint). What is missing is the System.Void (notice there is no pointer at the end) aka the void type in F#. However the integration will be challenging due the unit type mapping / overlap (e.g.: chkSystemVoidOnlyInTypeof does not seems to be accidental as it will allow only the typeof<System.Void> usage).

> typeof<nativeptr<int>>.FullName;;
val it : string = "System.IntPtr"

> typeof<System.Void>.IsValueType;;    
val it : bool = true

[krauthaufen]

Okay then maybe just allow nativeptr<voidptr> (and still not allowing voidptr inside unmanaged structs/etc.) since it gets compiled to nativeint anyways? The Problem I'm currently facing is actually quite severe since there is a C# method I simply can't invoke from F# (expecting a nativeptr<voidptr>)
Any thoughts?

[zpodlovics]

You can always store an untyped pointer (nativeint) in the struct and have some helper methods / functions to map it to a proper type (worst case scenario is to call for an C# helper). What is the C# signature that you want to call (you can use simplified struct and some generic names)?

[krauthaufen]

I didn't look at the source yet but the F# type hover shows me a nativeptr<voidptr> which seems to be impossible to produce from F#

[krauthaufen]

I can certainly work around that using a micro C# library but nonetheless it would be great to see that fixed somewhen...
What's really ironic is, that I only want to pass a null pointer 😜

[dsyme]

This is by design for F# 6, so perhaps add a language suggestion