Question How to iterate enum values with Burst?

Let's say I have an enum like the following:

Code (CSharp):

1. public enum Direction
2. {
3.     North,
4.     East,
5.     South,
6.     West,
7. }

Ideally, I would like to write code like this:

Code (CSharp):

1. foreach (Direction direction in Enum.GetValues(typeof(Direction)))
2. {
3.     // ...
4. }

However, since Burst does not support Enum methods (yet?), I'm trying to find the best alternative. The first thing I tried was creating a static array field that had contained all of the enum values, like so:

Code (CSharp):

1. public static readonly Direction[] AllDirections = {
2.     Direction.North,
3.     Direction.East,
4.     Direction.South,
5.     Direction.West
6. };

This still isn't great, as I have to keep this array in sync with the enum, but its good enough for me. However, this results in the following error when I try to call it from a burst-compiled Entities.ForEach query:

I tried changing the enum type to be explicit as int or byte but that didn't help. I'm not sure if this is a bug in burst or some limitation that I'm not aware of. The only workaround I found was to create a wrapper struct type like so:

Code (CSharp):

1. public struct DirectionWrapper
2. {
3.     public static readonly DirectionWrapper[] AllDirections =
4.     {
5.         new DirectionWrapper { Value = Direction.North },
6.         new DirectionWrapper { Value = Direction.East },
7.         new DirectionWrapper { Value = Direction.South },
8.         new DirectionWrapper { Value = Direction.West },
9.     };
10.  
11.     public Direction Value;
12.  
13.     public static implicit operator Direction(DirectionWrapper wrapper) => wrapper.Value;
14. }

I can then iterate directions like this:

Code (CSharp):

1. foreach (Direction direction in DirectionWrapper.AllDirections)
2. {
3.     // ...
4. }

This works, but it seems like there has to be a better option. Any suggestions? Thanks!

 

You can initialize those array at runtime using a static constructor

 

Burst has no problem with enums, since these are just numbers.
You can put enum even in IComponentData.

But since you have

Code (CSharp):

1. public enum Direction
2. {
3.     North = 0,
4.     East = 1,
5.     South = 2,
6.     West = 3,
7. }
8.  
9. struct DirectionComponent : IComponentData { public Direction direction } ;
10.  

You can access enum values in bursted jobs by enum itself, or by assigned value.

Code (CSharp):

1. var directionComponent = new DirectionComponent () { direction = Direction.South }
2. // OR
3. var directionComponent = new DirectionComponent () { direction = (Direction) 2 }

Or make DirectionComponent to store int.

And if you just want to iterate, so knowing number of elements in enum, you can run for loop.

 

You should be fine accessing this inside burst. Maybe you were assigning it to a local variable?

This is okay

Code (CSharp):

1. for( int i = 0; i < AllDirections.Length; ++i )

This is not

Code (CSharp):

1. var arr = AllDirections;
2. for(int i = 0; i < arr.Length; ++i)

But like Antypodish said you could just assign your enums numbers 0-3, then do a regular for loop and convert the index to your enum value.

 

A useful trick is to assign a known value as the final value inside the enum.

Code (CSharp):

1. public enum Direction
2. {
3.     North,
4.     East,
5.     South,
6.     West,
7.     Max
8. }

So that you can do this:

Code (CSharp):

1. for (Direction direction = 0; direction < Direction.Max; direction++)
2. {
3.     Debug.Log($"Direction: {direction}");
4. }
5.  

Of course, this only works if all values are sequential and start at 0.

 

I should have clarified. The code that produces the error in my original post is when I try to do a

foreach

loop over AllDirections. A normal for loop that looks up the Direction from the static array works just fine.

Specifically, let's say I have the following:

Code (CSharp):

1. public struct DirectionHelper
2. {
3.     public static readonly Direction[] AllDirections =
4.     {
5.         Direction.North,
6.         Direction.East,
7.         Direction.South,
8.         Direction.West
9.     };
10. }
11.  

This works fine:

Code (CSharp):

1. for (int i = 0; i < DirectionHelper.AllDirections.Length; i++)
2. {
3.     Direction direction = DirectionHelper.AllDirections[i];
4.     // ...
5. }

But this produces a burst error:

Code (CSharp):

1. foreach (Direction direction in DirectionHelper.AllDirections)
2. {
3.     // ...
4. }

So I guess the problem is that burst doesn't support GetEnumerator() on enum arrays?

Burst 1.4.1
Unity 2020.2.0b9

That is a great idea, thanks! Allows me to remove my static "max" fields that I had added to do the same thing, but were easily getting out of sync.

 

@tim_jones Awesome, thanks!

I also greatly appreciate the other ideas mentioned in this thread.