ISubject<TSource, TResult> public interface ISubject<TSource, TResult> : IObserver<TSource>, IObservable<TResult> Documentation Code using System.Runtime.CompilerServices; namespace System.Reactive.Subjects { [NullableContext(2)] public interface ISubject<in TSource, out TResult> : IObserver<TSource>, IObservable<TResult> { } }