# AddSystem<T>(World)

> Obsolete. Use World.CreateSystem instead.

## Definition

* **Type:** Method
* **Namespace:** [Unity.Entities](/engine/7000.0/script-reference/unity/entities.md)
* **Assembly:** UnityEngine.EntitiesModule

> **Warning:**
>
> **Deprecated.** Use World.CreateSystem instead

```csharp
public static SystemHandle AddSystem<T>(this World self) where T : unmanaged, ISystem
```

### Parameters

**** (\[World]\(/engine/7000.0/script-reference/unity/entities/world)): The World

### Returns

| Type                                                                           | Description |
| ------------------------------------------------------------------------------ | ----------- |
| [SystemHandle](/engine/7000.0/script-reference/unity/entities/systemhandle.md) |             |