C# 9.0 Function Pointers

Unity Engine
,
1

First off, I want to say I’ve been keeping an eye on the C# 9 function pointers, and I really appreciate the efforts the scripting team has made so far with its support. I was excited to use them in Burst with the hope that they can be used to overcome the generic delegate limitation when using FunctionPointer in non-bursted code.

Currently running Unity 2021.2.0a13 with Burst 1.6.0-pre.2, I am running into
```Burst error BC1054: Unable to resolve type `method System.Int32 *(System.Int32). Reason: Unknown.````

Here’s a snip of the failing Job:

[BurstCompile]
public unsafe struct CallFuncJob : IJob
{
    [NativeDisableUnsafePtrRestriction]
    public IntPtr FuncPtr;
    public NativeArray<int> In;
    public NativeArray<int> Out;

    public void Execute()
    {
        Out[0] = ((delegate* unmanaged[Cdecl]<int, int>)FuncPtr)(In[0]);
    }
}
2

Ideally, I hope it can support something like this:

public unsafe struct BurstFunc<T, TResult>
  where T : struct
  where TResult : struct
{
  readonly delegate* unmanaged[Cdecl]<T, TResult> _ptr;

  public BurstFunc(IntPtr ptr)
  {
    _ptr = ptr;
  }

  public TResult Invoke(T arg0) => _ptr(arg0);

  public static BurstFunc<T, TResult> Compile(Func<T, TResult> func)
  {
    var ptr = BurstCompiler.CompileFunctionPointer(func);
    return new BurstFunc<T, TResult>(ptr.Value);
  }
}
3

Yes, function pointers should be fixed/supported for Burst 1.6

Note that Burst compilation of open generics is not supported for delegate (they are not supported by .NET with interop either see this)

4

There’s also this now that I am looking into after a tip from elsewhere on these here fora:
https://docs.unity3d.com/Packages/com.unity.burst@1.6/manual/docs/AdvancedUsages.html#function-pointers