Proposal: ITask and ITask<T> interfaces

[Joy-less]

Currently, it can be very tricky to work with tasks in reflection. For example, if you have a Task<T> cast to an object, there is no way to get the result without reflection. Additionally, there is no way to handle Task and ValueTask at the same time. An ITask interface could solve both problems.

Before

object? obj = GetObject();
if (obj is Task task) {
    if (task.GetType().IsGenericType) {
        object? result = task.GetType().GetProperty(nameof(Task<object>.Result))!.GetValue(task);
    }
}
else if (obj is ValueTask valueTask) {
    if (valueTask.GetType().IsGenericType) {
        object? result = valueTask.GetType().GetProperty(nameof(ValueTask<object>.Result))!.GetValue(valueTask);
    }
}

After

object? obj = GetObject();
if (obj is ITask task) {
    if (task.TryGetResult(out object? result)) {
        // ...
    }
}

A proposal already exists to make Task covariant, meaning Task<string> could be cast to Task<object>. However, this proposal would also handle ValueTask, and any other type of Task added in the future.

ITask would look something like this:

namespace System.Threading.Tasks;

public interface ITask {
    public bool TryGetResult(out object? result);
    public bool HasResult();
    public TaskAwaiter GetAwaiter();
}

public interface ITask<T> : ITask {
    public T GetResult();
    public new TaskAwaiter<T> GetAwaiter();
}

Both Task and ValueTask would inherit from ITask. Additionally, asynchronous functions would be able to return ITask instead of Task or ValueTask.

[HaloFour]

This is an API request and should be made to the runtime repository.

[Joy-less]

Apologies. It has been reopened here: dotnet/runtime#110930