Creating a task wrapper around an existing object

Question

I have a method which returns a Task where the implementation may or may not need to perform a slow operation in order to retrieve the result. I would like to be able to si

Answer 1

If you have a synchronous version of the method that returns the result you can do the following

Task<String>(()=> Hello(Name));

The hello method would look like below.

public String Hello(String Name)
{
   return "Hello " + Name;
}

Answer 2

Beginning with .NET 4.5, you can use the Task.FromResult<T>() static method for exactly this purpose:

return Task.FromResult(_Cache[key]);

Answer 3

You could use a TaskCompletionSource<TResult>:

var tcs = new TaskCompletionSource<Foo>();
tcs.SetResult(_Cache[key]);
return tcs.Task;

(Note that if _Cache is a Dictionary<TKey, TValue> you could use TryGetValue to make it a single lookup.)