wave4-systembase-with-inner-ijobentity

SystemBase with Inner IJobEntity

Intent

Use managed SystemBase class when the system itself requires managed resources, while delegating hot-path work to Burst-compiled inner IJobEntity structs.

Use When

• System must hold managed references (physics callbacks, coroutine coordinators, managed subscene access, interface references).
• Multiple jobs per OnUpdate need to share implicit dependency chain.

Avoid When

System has no managed needs — use partial struct : ISystem with [BurstCompile] on OnUpdate (lower overhead, Burst-compilable scheduling).

Senior Pattern

public partial class AnimationSystem : SystemBase
{
    [BurstCompile]
    partial struct UpdateFrameJob : IJobEntity
    {
        public float DeltaTime;

        [BurstCompile]
        public void Execute(ref AnimationState anim, in AnimationClipRef clipRef)
        {
            anim.Time += DeltaTime;
        }
    }

    [BurstCompile]
    partial struct ApplyTransformJob : IJobEntity
    {
        [BurstCompile]
        public void Execute(ref LocalTransform transform, in AnimationState anim)
        {
            // apply animation state to transform
        }
    }

    protected override void OnUpdate()
    {
        float dt = SystemAPI.Time.DeltaTime;
        new UpdateFrameJob { DeltaTime = dt }.ScheduleParallel();
        new ApplyTransformJob().ScheduleParallel();
        // SystemBase.Dependency auto-chains between sequential ScheduleParallel calls
    }
}

Anti-Patterns

• Marking OnUpdate with [BurstCompile] — SystemBase.OnUpdate is virtual managed; Burst cannot compile it.
• Two inner jobs writing the same component without chaining — SystemBase auto-chains sequential ScheduleParallel calls within one OnUpdate, but manually completing Dependency between calls breaks the chain.
• Preferring SystemBase for simplicity when no managed context is needed — adds virtual dispatch overhead every frame for no benefit.

Runtime Risks

• Multiple ScheduleParallel calls on same system auto-chain via Dependency property; manually completing Dependency between calls breaks the chain.
• SystemBase does not support [BurstCompile] on OnUpdate; only inner job structs can be Burst-compiled.