Question Generic type parameter for IEnumerable not supported?

Hello,

I tried to provide IEnumerable as a generic type parameter for a method, but that does not work. Is this not supported by Burst or is there a way to get it work?

Thats the code:

Code (CSharp):

1. public interface INativeSwappingStructList<TElement> : IDisposable where TElement : unmanaged
2. {
3.   void AddRange<TEnumerable>(int swapIndex, TEnumerable addedElements) where TEnumerable : unmanaged, IEnumerable<TElement>;
4. }  
5.  
6. [BurstCompile]
7. public struct NativeSwappingStructListCore<TElement> : INativeSwappingStructList<TElement> where TElement : unmanaged
8. {
9.   [BurstCompile]
10.   public void AddRange<TEnumerable>(int swapIndex, TEnumerable addedElements) where TEnumerable : unmanaged, IEnumerable<TElement>
11.   {
12.     foreach (var element in addedElements)
13.     {
14.     }
15.   }
16. }
17.  
18. private struct MyStruct : IEquatable<MyStruct>
19. {
20.   public int X;
21.   public float F;
22.   // ...
23. }
24.  
25. // Called within other burst compiled code:
26. NativeArray<MyStruct> array = new(2, Allocator.Temp);
27. array[0] = new();
28. array[1] = new();
29.  
30. NativeSwappingStructListCore<MyStruct> list = new(/* ... */);
31. list.AddRange(0, array);

Thats the error:

NativeArray itself supports IEnumerable<T>:

Code (CSharp):

1. public struct NativeArray<T> : IDisposable, IEnumerable<T>, IEnumerable, IEquatable<NativeArray<T>>
2.     where T : struct

 

First thing to check: does it compile without Burst?Does it also work correctly?

I read somewhere that Burst does not support scheduling generic jobs from generic methods. Maybe that has something to do with it.
I would simplify this test to see where the issue is coming from. Like making AddRange a static method in a non generic class.

 

Yes, thats fine C# code. In this case I want to circumvent the not allowed managed type restriction of Burst. The use of IEnumerable<TElement> instead of TEnumerable would clearly not work, because IEnumerable (interfaces in general) is a managed type. Also this technique of using generic types for interfaces avoids boxing of structs in plain C#, so its also having its purpose.

Thanks for looking into that issue.

 

Thanks for looking into my issue and stating a workaround. This is indeed interessting that the IL-Code of Roslyn still does virtual calls for members of IEnumerable supplied as generic type parameter. So I will stick to your stated workaround to be Burst compatible.

 

Wanted to point out another alternative that may work. Instead of

foreach

, you can use

Code (CSharp):

1. var enumerator = enumerable.GetEnumerator();
2. while (enumerator.MoveNext())
3. {
4.   var item = enumerator.Current;
5. }