Csharp Async Await Task Yield

🔹 async and await — Asynchronous Programming

✅ Goal:

Run non-blocking code (like loading a file or waiting for a web request) without freezing your app.

⸻

🔧 async keyword • Marks a method as asynchronous. • It allows using await inside that method. • It usually returns Task, Task<T>, or void (for event handlers).

public async Task DoSomethingAsync() 
{
	await Task.Delay(2000); // Imagine there's a mission of HTTP request need 2 seconds to complete. Non-blocking.
	Debug.Log("Done HTTP mission");
}

⸻

🔧 await keyword • Waits for a Task to finish, but doesn’t block the main thread. • Resumes the method after the awaited task completes.

await Task.Delay(1000); // Delays for 1 second without freezing; Imitating HTTP request

⸻

🔹 Task and Task<T> — Represent Future Results

✅ Goal:

Run methods in the background, or represent operations that complete later.

public async Task<int> GetScoreAsync() 
{
	await Task.Delay(1000);//Imitating HTTP request
	return 42;
}

•	Task: returns nothing
•	Task<T>: returns value T when done

⸻

🔹 yield — Generator Keyword

✅ Goal:

Create lazy iterators (one item at a time), useful for loops, state machines, or coroutines.

public IEnumerable<int> GetNumber() 
{
	yield return 1;
	yield return 2;
	yield return 3;
}

•	yield return: gives one value at a time
•	yield break: ends the sequence

🧠 In Unity:

Unity’s IEnumerator coroutines (used with StartCoroutine) rely on yield:

IEnumerator WaitExample()
{
    yield return new WaitForSeconds(2);
    Debug.Log("2 seconds passed");
}

⸻

🔄 Summary Table

Keyword	Purpose	Common Return Type	Example Use
async	Marks a method as asynchronous	Task, Task	async Task LoadData()
await	Waits for a Task to finish	N/A	await LoadData()
Task	Represents async operation	Task, Task	return Task.Delay(1000)
yield	Generates values lazily	IEnumerable, IEnumerator	yield return x

⸻

🧪 Want to test it?

Here’s a quick Unity example:

private async void Start()
{
    Debug.Log("Before wait");
    await Task.Delay(3000); // Doesn't freeze Unity. Imitating this is a http request
    Debug.Log("After 3 seconds");
}

And a coroutine version with yield:

private void Start()
{
    StartCoroutine(MyCoroutine());
}

private IEnumerator MyCoroutine()
{
    Debug.Log("Before wait");
    yield return new WaitForSeconds(3); //Imitating this is a http request
    Debug.Log("After 3 seconds");
}