// return async-value.(or you can use `UniTask`(no result), `UniTaskVoid`(fire and forget)).
return (asset as TextAsset)?.text ?? throw new InvalidOperationException("Asset not found");
}
```
`UniTask<T>`
---
UniTask feature rely on C# 7.0([task-like custom async method builder feature](https://github.com/dotnet/roslyn/blob/master/docs/features/task-types.md)) so required Unity version is after `Unity 2018.3`.
Why UniTask(custom task-like object) is required? Because Task is too heavy, not matched to Unity threading(single-thread). UniTask does not use thread and SynchronizationContext because almost Unity's asynchronous object is automaticaly dispatched by Unity's engine layer. It acquires more fast and more less allocation, completely integrated with Unity.
You can await `AsyncOperation`, `ResourceRequest`, `UnityWebRequestAsyncOperation`, `IEnumerator` and others when using `UniRx.Async`.
`UniTask.Delay`, `UniTask.Yield`, `UniTask.Timeout` that is frame-based timer operators(no uses thread so works on WebGL publish) driven by custom PlayerLoop(Unity 2018 experimental feature). In default, UniTask initialize automatically when application begin, but it is override all. If you want to append PlayerLoop, please call `PlayerLoopHelper.Initialize(ref yourCustomizedPlayerLoop)` manually.
> Before Unity 2019.3, Unity does not have `PlayerLooop.GetCurrentlayerLoop` so you can't use with Unity ECS package in default. If you want to use with ECS and before Unity 2019.3, you can use this hack below.
```csharp
// Get ECS Loop.
var playerLoop = ScriptBehaviourUpdateOrder.CurrentPlayerLoop;
// Setup UniTask's PlayerLoop.
PlayerLoopHelper.Initialize(ref playerLoop);
```
`UniTask.WhenAll`, `UniTask.WhenAny` is like Task.WhenAll/WhenAny but return type is more useful.
`UniTask.ctor(Func<UniTask>)` is like the embeded [`AsyncLazy<T>`](https://blogs.msdn.microsoft.com/pfxteam/2011/01/15/asynclazyt/)
```csharp
public class SceneAssets
{
public readonly UniTask<Sprite> Front;
public readonly UniTask<Sprite> Background;
public readonly UniTask<Sprite> Effect;
public SceneAssets()
{
// ctor(Func) overload is AsyncLazy, initialized once when await.
// and after it, await returns zero-allocation value immediately.
Front = new UniTask<Sprite>(() => LoadAsSprite("foo"));
Background = new UniTask<Sprite>(() => LoadAsSprite("bar"));
Effect = new UniTask<Sprite>(() => LoadAsSprite("baz"));
}
async UniTask<Sprite> LoadAsSprite(string path)
{
var resource = await Resources.LoadAsync<Sprite>(path);
return (resource as Sprite);
}
}
```
If you want to convert callback to UniTask, you can use `UniTaskCompletionSource<T>` that is the lightweight edition of `TaskCompletionSource<T>`.
```csharp
public UniTask<int> WrapByUniTaskCompletionSource()
{
var utcs = new UniTaskCompletionSource<int>();
// when complete, call utcs.TrySetResult();
// when failed, call utcs.TrySetException();
// when cancel, call utcs.TrySetCanceled();
return utcs.Task; //return UniTask<int>
}
```
You can convert Task -> UniTask: `AsUniTask`, `UniTask` -> `UniTask<AsyncUnit>`: `AsAsyncUnitUniTask`(this is useful to use WhenAll/WhenAny), `UniTask<T>` -> `UniTask`: `AsUniTask`.
If you want to convert async to coroutine, you can use `UniTask.ToCoroutine`, this is useful to use only allow coroutine system.
Reusable Promises
---
Exception handling
---
`OperationCanceledException` and `UniTaskScheduler.UnobservedTaskException`, `UniTaskVoid`. and what is `UniTask.SuppressCancellationThrow`.
