Default value for native container (no memory allocation)

[onyx oyster]

Is this possible to use some sort of default value for native containers? For normal arrays I would use null but since they are value types it does not work 😦
Otherwise I don't know how to initialize my jobs output NativeArrays when I don't know their size when constructing the job (the size is calculated inside the job).

The only thing I can think of would be :
output = new NativeArray<int>(0, Allocator.TempJob);
output.Dispose()
But that looks horrible 😅
That does not even work 😫

Or should I make another job to calculate the size and run that job first?

[sterile hearth]

We use this property to verify if the native container is initialized or not

https://docs.unity3d.com/ScriptReference/Unity.Collections.NativeArray_1.IsCreated.html

[onyx oyster]

Thank you but my question is how can I create a not (yet) initialized container?

Because when constructing a struct, all variables have to have a value if I am correct

[sterile hearth]

Ah, then you can use this method in CollectionHelper

https://docs.unity3d.com/Packages/com.unity.collections@2.2/api/Unity.Collections.CollectionHelper.html#Unity_Collections_CollectionHelper_CreateNativeArray__2_System_Int32___1__Unity_Collections_NativeArrayOptions_

CreateNativeArray<T, U>(Int32, ref U, NativeArrayOptions)

And pass in this value

https://docs.unity3d.com/2022.2/Documentation/ScriptReference/Unity.Collections.NativeArrayOptions.UninitializedMemory.html

[onyx oyster]

With which allocator?

[sterile hearth]

Btw, this code will give you a native array of 10 elements, and each element has a default value of 0

var arr = new NativeArray<int>(10, Allocator.Temp);

[onyx oyster]

That returns an error saying that I can't use Temp memory for scheduling a job.
And if I use TempJob instead, I have to dispose it, which I can't do in the job 😦

[sterile hearth]

[BurstCompile]
public void OnUpdate(ref SystemState state)
{
    var arr = new NativeArray<int>(10, Allocator.TempJob);
    var job = new MyJob { arr = arr };
    var dependency = job.Schedule(state.Dependency);
    arr.Dispose(dependency);

    state.Dependency = dependency;
}

[BurstCompile]
private partial struct MyJob : IJob
{
    public NativeArray<int> arr;

    public void Execute()
    {
    }
}

I've just double-checked it, you can create NativeArray with NativeArrayOptions.UninitializedMemory parameter. You don't have to use CollectionHelper.

[onyx oyster]

Alright I will try this, thank you!

[sterile hearth]

I use CollectionHelper when I want to use the state.WorldUpdateAllocator. For which I don't have to worry about disposing the array.

[BurstCompile]
public void OnUpdate(ref SystemState state)
{
    var arr = CollectionHelper.CreateNativeArray<int>(10, state.WorldUpdateAllocator);
    var job = new MyJob { arr = arr };
    state.Dependency = job.Schedule(state.Dependency);
}

[onyx oyster]

Yes it worked thank you! 🙂

[verbal plover]

use WorldUpdateAllocator

or right

already answered