What is the use for Task.FromResult<TResult> in C#

Question

There are two common use cases I've found:

1. When you're implementing an interface that allows asynchronous callers, but your implementation is synchronous.
2. When you're stubbing/mocking asynchronous code for testing.

One example would be a method that makes use of a cache. If the result is already computed, you can return a completed task with the value (using Task.FromResult). If it is not, then you go ahead and return a task representing ongoing work.

Cache Example: Cache Example using Task.FromResult for Pre-computed values

Use it when you want to create an awaitable method without using the async keyword. I found this example:

public class TextResult : IHttpActionResult
{
    string _value;
    HttpRequestMessage _request;

    public TextResult(string value, HttpRequestMessage request)
    {
        _value = value;
        _request = request;
    }
    public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
    {
        var response = new HttpResponseMessage()
        {
            Content = new StringContent(_value),
            RequestMessage = _request
        };
        return Task.FromResult(response);
    }
}

Here you are creating your own implementation of the IHttpActionResult interface to be used in a Web Api Action. The ExecuteAsync method is expected to be asynchronous but you don't have to use the async keyword to make it asynchronous and awaitable. Since you already have the result and don't need to await anything it's better to use Task.FromResult.

From MSDN:

This method is useful when you perform an asynchronous operation that returns a Task object, and the result of that Task object is already computed.

http://msdn.microsoft.com/en-us/library/hh228607.aspx