How to Design Fluent Async Operations?

Question

Async operations do not seem to play well with fluent interfaces which I prefer to code in. How can Asynchrony be combined with Fluent?

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Sample: I have two methods that previously returned a MyEntity but do not play well when change to Async. After I asyncfy them I have to await the result of the tasks, but I have to do that for each step added:

MyEntity Xx = await(await FirstStepAsync()).SecondStepAsync();

There has to be a better way.

Answer 1

Some of the answers that deal with continuations are forgetting that fluent works on concrete instances that are returned from each method.

I have written a sample implementation for you. The asynchronous work will start immediately on calling any of the DoX methods.

public class AsyncFluent
{
    /// Gets the task representing the fluent work.
    public Task Task { get; private set; }

    public AsyncFluent()
    {
        // The entry point for the async work.
        // Spin up a completed task to start with so that we dont have to do null checks    
        this.Task = Task.FromResult<int>(0);
    }

    /// Does A and returns the `this` current fluent instance.
    public AsyncFluent DoA()
    {
        QueueWork(DoAInternal);
        return this;
    }

    /// Does B and returns the `this` current fluent instance.
    public AsyncFluent DoB(bool flag)
    {
        QueueWork(() => DoBInternal(flag));
        return this;
    }

    /// Synchronously perform the work for method A.
    private void DoAInternal()
    {
        // do the work for method A
    }

    /// Synchronously perform the work for method B.
    private void DoBInternal(bool flag)
    {
        // do the work for method B
    }

    /// Queues up asynchronous work by an `Action`.
    private void QueueWork(Action work)
    {
        // queue up the work
        this.Task = this.Task.ContinueWith<AsyncFluent>(task =>
            {
                work();
                return this;
            }, TaskContinuationOptions.OnlyOnRanToCompletion);
    }
}