Why is Task not co-variant?

Question

class ResultBase {}
class Result : ResultBase {}

Task GetResult() {
    return Task.FromResult(new Result());
}

The compiler tel

Answer 1

I realize I'm late to the party, but here's an extension method I've been using to account for this missing feature:

/// 

/// Casts the result type of the input task as if it were covariant
/// 
/// The original result type of the task
/// The covariant type to return
/// The target task to cast
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static async Task AsTask(this Task task) 
    where T : TResult 
    where TResult : class
{
    return await task;
}

This way you can just do:

class ResultBase {}
class Result : ResultBase {}

Task GetResultAsync() => ...; // Some async code that returns Result

Task GetResultBaseAsync() 
{
    return GetResultAsync().AsTask();
}