using System.Runtime.CompilerServices; namespace System.Reactive.Joins { [NullableContext(1)] [Nullable(0)] public class Pattern<[Nullable(2)] TSource1> : Pattern { internal IObservable<TSource1> First { get; } internal Pattern(IObservable<TSource1> first) { First = first; } public Plan<TResult> Then<[Nullable(2)] TResult>(Func<TSource1, TResult> selector) { if (selector == null) throw new ArgumentNullException("selector"); return new System.Reactive.Joins.Plan<TSource1, TResult>(this, selector); } } }