なんかしぬやつ.cs

using System;
using System.Reactive.Linq;
using System.Reactive.Subjects;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var subject = new Subject<int>();
            Observable.Return(0)
                .SelectMany(_ => subject.AsObservable().FirstAsync())
                .Do(_ => subject.OnNext(0))
                .Subscribe(x => Console.WriteLine("result:" + x));

            subject.OnNext(999); // StackOverflowException!!!
        }

        static void Test1()
        {
            var subject = new Subject<int>();
            Observable.Return(0)
                //.SelectMany(_ => subject.AsObservable().FirstAsync())
                .SelectMany(async _ => await subject.AsObservable().FirstAsync()) // async/await
                .Do(_ => subject.OnNext(0))
                .Subscribe(x => Console.WriteLine("result:" + x));

            subject.OnNext(999); // これはいける result:999
        }

        static void Test2()
        {
            var subject = new Subject<int>();
            Observable.Return(0)
                //.SelectMany(_ => subject.AsObservable().FirstAsync())
                .SelectMany(_ => subject.AsObservable().Take(1)) // Take First
                .Do(_ => subject.OnNext(0))
                .Subscribe(x => Console.WriteLine("result:" + x));

            subject.OnNext(999); // これもいける result:999
        }
    }
}