System says struct is blittable, unity say's struct isn't blittable

Heyjo,
I have created a struct like this:

Code (CSharp):

1. [StructLayout(LayoutKind.Sequential)]
2. public struct Foo
3. {
4.     public int i;
5.  
6.     [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)]
7.     public int[] bar;
8. }

This should be a blittable struct. I checked that with the following function. (thanks to StackOverflow):

Code (CSharp):

1. public static class BlittableHelper<T>
2.     {
3.         public static readonly bool IsBlittable;
4.  
5.         static BlittableHelper()
6.         {
7.             try
8.             {
9.                 // Class test
10.                 if (default(T) != null)
11.                 {
12.                     // Non-blittable types cannot allocate pinned handle
13.                     GCHandle.Alloc(default(T), GCHandleType.Pinned).Free();
14.                     IsBlittable = true;
15.                 }
16.             }
17.             catch { }
18.         }
19.     }

In addition the call:

Code (CSharp):

1. Debug.Log(BlittableHelper<Foo>.IsBlittable);

The debugger gives me back true. So far so good. But now when I try to put this struct in a NativeList, the NativeList tells me that this struct is not blittable.

Code (CSharp):

1. NativeList<Foo> t = new NativeList<Foo>(10, Allocator.Persistent);

What am I doing wrong? Does anyone have an idea?

 

From the Stackoverflow entry you got this from: Note that this won't work on Mono, because GCHandle.Alloc doesn't throw an exception for non blittable types.

A reference to a managed array is not blittable.

Using C# 7.3 you could make your check at compile time. The unmanaged generic constraint only matches blittable types:

Code (CSharp):

1. public static class BlittableHelper<T> where T : unmanaged
2. {
3.     public static readonly bool IsBlittable = true;
4. }
5.  

 

Unity has a built in method for checking Blittable (which is what NativeList uses)

UnsafeUtility.IsBlittable<T>()

The first require to determine if something is Blittable in Unity ECS is if it is a struct.
Arrays are not.

 

Not all unmanaged types are blittable e.g. bool