Help: Updating an Element in a NativeList

Hi All,
I'm trying to do something very simple - update an existing element in a NativeList. I understand that a struct is a value type. I can get a copy of the struct and update a property, but I can't assign it back at the same index (required as these are mesh vertices).
I get "Cannot modify the return value of 'AreaJob.VertexList' because it is not a variable".

Code (CSharp):

1.         private int SetVertexIndex(float3 point, int external)
2.         {
3.             int index;
4.             if (vertexCheck.ContainsKey(point))
5.             {
6.                 index = vertexCheck[point];
7.  
8.                 //Copy of the Vertex struct.
9.                 Vertex vertex = VertexList[index];
10.                 //Update a property. This works.
11.                 vertex.Usage += 1;
12.                 //Assign the vertex copy back to the list. This doesn't work.
13.                 VertexList[index] = vertex;
14.  
15.                 //Not much documentation on this extension but apparently returns a ref??
16.                 //Still didn't work.
17.                 //VertexList.ElementAt(index).Usage += 1;
18.             }
19.             else
20.             {
21.                 index = VertexList.Length;
22.                 vertexCheck.TryAdd(point, index);
23.                 VertexList.Add(new Vertex(point, external));        
24.             }
25.             return index;
26.         }

This is so simple I think I must be very stupid. Apologies for that. Any help appreciated.

 

It should work. Something else is wrong. Hard to say what though without more code and a more complete error message.

Also, yes, ElementAt returns a ref. It works as you would expect it to.

 

Thanks. But I'm not sure where else there could be an issue. Without that code to update the existing element, it runs perfectly and produces beautiful procedural meshes.



The error message is a Console/IDE error message and there is nothing more verbose.
The only thing I could think of was that the NativeList is external to the job but I tried to change it so it's instantiated in the Job but it still doesn't compile. Plus everything else works and I can Add to the list quite happily.
So VertexList.ElementAt(index).Usage += 1; would be the correct way to use it in this case?

 

VertexList is property, copy it's value to local variable

Code (CSharp):

1. var v = VertexList;
2. v[index] = vertex;

 

Yes. That's what I was suspecting too. That solution works. ElementAt will also work.

 

This didn't work either.

Code (CSharp):

1.  
2.                 //Copy of the Vertex struct.
3.                 var v = VertexList;
4.                 Vertex vertex = v[index];
5.                 ////Update a property. This works.
6.                 vertex.Usage = 10;
7.                 //Assign the vertex copy back to the list. This doesn't work.
8.                 v[index] = vertex;
9.  
10.                 //Not much documentation on this extension but apparently returns a ref??
11.                 //Still didn't work.
12.                 //v.ElementAt(index).Usage += 1;

 

Vertex vertex = VertexList[index];
vertex.Value = Able;
VertexList[index] = vertex;

 

Can we see the definition of VertexList? Something really funky seems to be happening.

As for ElementAt:

Code (CSharp):

1. ref var vertex = ref VertexList.ElementAt(index);
2. vertex.Usage += 1;

 

Ok, as Arbex said, it was the fact that VertexList was an AutoProperty that was messing it up (as well as me). Thanks all for the suggestions.
And in fact after changing it.

Code (CSharp):

1. vertexList.ElementAt(index).Usage += 1;

worked just fine.