Need a workaround to access ReadOnlySpan<T> inside a function that returns an IEnumerable

while dealing with native code interop I decided it was the time to learn and try new Span features of the C# language. Although with many trials, everything was going perfectly fine until I come to the final stage of my very long function for which I insert below just a minimal reproducible sample:

    [DllImport(dll, SetLastError = true)]
    internal static extern void GetNativeData(out byte lpBuffer, int size, out bytesRead);

    ReadOnlySpan<T> ReadArray<T>(ReadOnlySpan<byte> buf, int Length) where T : unmanaged
    {
        var size = Length * Unsafe.SizeOf<T>();
        if (buf.Length < size)
            buf = new byte[size];
            GetNativeData(out MemoryMarshal.GetReference(buf), size, out int read));
            Dh.CreateError(ReadMemoryErr);
        
        return MemoryMarshal.Cast<byte, T>(buf.Slice(0, size));
    }

    static IEnumerable<MyClass> GetResult()
    {
        // Here I allocate a buffer
        Span<byte> buf = new byte[1000];

        // After a long serie of calls to unmanaged DLL functions I end up with something like this:
        ReadOnlySpan<uint> uintRes = data.ReadArray<uint>(buf, 10);
        ReadOnlySpan<ushort> shortRes = data.ReadArray<ushort>(buf, 10);
        for (int i = 0; i < uintRes.Length; i++)
        {
           // Any access to spans inside this loop result in Error CS4013
           string r = GetFunRes(uintRes[i]);
           IntPtr r2 = GetFunRes2(shortRes[i]);
           yield return new MyClass() { Prop1 = r, Prop2 = r2 };
        }
    }

The error I get is

Error CS4013: Instance of type 'Span' cannot be used inside a nested function, query expression, iterator block or async method

Now, I have read that there are workarounds for this. The articles only shows usage for async methods, but it also states that applies to iterators. Unfortunately I have not been able to make this work. I only need to read specific elements of the span and then, yield a result that does not contains any element or reference to the span. It's just that whatever I try to, as soon as I try to access something the compiler fails.

I have read about Memory<T>, may be that this one could work, but I have some concerns because I have read that the performance is dramatically reduced. People also recommend Span at the first place. I hope I can find a solution because otherwise I will have to restart from scratch my project and rewrite everything because now is tightly tied to Span.

Thanks in advance for your help

@00110001:

var uintRes = data.ReadArray<uint>(buf, 10).ToArray();

I know that this will work, but I suppose that it will make Span usage useless along with the new generics unmanaged features I am trying to take advantage of (ReadArray<T>). If I am not wrong, calling ToArray() it's the same of the old Marshaling style where a new copy is created for each call:

internal static extern void GetNativeData(out uint[] lpBuffer, int size, out bytesRead);

@Ian Kemp This is how I tried the workaround mentioned in the article:

int len = uintRes.Length;
for (int i = 0; i < len; i++)
{
   var res = ParseData(i);
   if (res == ExpectedResult())
      yield return res;
}
MyClass ParseData(int index)
{
     // CS8175: Cannot use ref local 'uintRes, shortRes' inside an anonymous method, lambda expression, or query expression
     string r = GetFunRes(uintRes[index]);
     IntPtr r2 = GetFunRes2(shortRes[index]);
     return new MyClass() { Prop1 = r, Prop2 = r2 };
}