Custom awaitable and awaiter types in C# 5.0 asynchronous

In C# 5.0 you can use the await keyword to await an awaitable object. But what is the minimum requirement for an object to be considered awaitable by C#? Interestingly there are no interfaces to be implemented in order to be considered awaitable!
Having a parameter-less method named GetAwaiter() which returns an awaiter object is the only convention for a type to be recognized awaitable by C#:

// This class is awaitable because it has the GetAwaiter method, provided MyAwaiter is an awaiter.
public class MyWaitable
{
    public MyAwaiter GetAwaiter()
    {
        return new MyAwaiter();
    }
}

Now the question is how to make a type awaiter? The minimum requirements for a type to be awiater are implementing the INotifyCompletion interface, and having the IsCompleted property and the GetResult method with the following signatures:

public class MyAwaiter : INotifyCompletion
{
    public void OnCompleted(Action continuation)
    {
        
    }

    public bool IsCompleted
    {
        get
        {
            return false;
        }
    }


    public void GetResult()
    {
       
    }
}
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2 thoughts on “Custom awaitable and awaiter types in C# 5.0 asynchronous

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