Difference between Task and async

C# provides two ways of creating asynchronous methods:

Method 1: 

static Task<string> MyAsyncTPL() {
  Task<string> result = PerformWork();
  return result.ContinueWith(t => MyContinuation());
}

Method 2:

static async Task<string> MyAsync() {
  string result = await PerformWork();
  return MyContinuation();
}

Both the above methods are async and achieves the same thing. So, when should I choose one method over the other? Are there any guidelines or advantages of using one over the other?

Jon Skeet
people
quotationmark

await is basically a shorthand for the continuation, by default using the same synchronization context for the continuation.

For very simple examples like yours, there's not much benefit in using await - although the wrapping and unwrapping of exceptions makes for a more consistent approach.

When you've got more complicated code, however, async makes a huge difference. Imagine you wanted:

static async Task<List<string>> MyAsync() {
    List<string> results = new List<string>();
    // One at a time, but each asynchronously...
    for (int i = 0; i < 10; i++) {
        // Or use LINQ, with rather a lot of care :)
        results.Add(await SomeMethodReturningString(i));
    }
    return results;
}

... that gets much hairier with manual continuations.

Additionally, async/await can work with types other than Task/Task<T> so long as they implement the appropriate pattern.

It's worth reading up more about what it's doing behind the scenes. You might want to start with MSDN.

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