Add Subscribe overload with riseOnSubscription parameter

src/R3/ObservableSubscribeExtensions.cs

@@ -28,6 +28,24 @@ public static IDisposable Subscribe<T>(this Observable<T> source, Action<T> onNe
         return source.Subscribe(new AnonymousObserver<T>(onNext, onErrorResume, onCompleted));
     }
 
+    [DebuggerStepThrough]
+    public static IDisposable Subscribe<T>(this Observable<T> source, Action<T> onNext, bool riseOnSubscription)
+    {
+        return source.Subscribe(new AnonymousObserver<T>(onNext, ObservableSystem.GetUnhandledExceptionHandler(), Stubs.HandleResult), riseOnSubscription);
+    }
+
+    [DebuggerStepThrough]
+    public static IDisposable Subscribe<T>(this Observable<T> source, Action<T> onNext, Action<Result> onCompleted, bool riseOnSubscription)
+    {
+        return source.Subscribe(new AnonymousObserver<T>(onNext, ObservableSystem.GetUnhandledExceptionHandler(), onCompleted), riseOnSubscription);
+    }
+
+    [DebuggerStepThrough]
+    public static IDisposable Subscribe<T>(this Observable<T> source, Action<T> onNext, Action<Exception> onErrorResume, Action<Result> onCompleted, bool riseOnSubscription)
+    {
+        return source.Subscribe(new AnonymousObserver<T>(onNext, onErrorResume, onCompleted), riseOnSubscription);
+    }
+
     // with state
 
     [DebuggerStepThrough]
@@ -47,6 +65,24 @@ public static IDisposable Subscribe<T, TState>(this Observable<T> source, TState
     {
         return source.Subscribe(new AnonymousObserver<T, TState>(onNext, onErrorResume, onCompleted, state));
     }
+
+    [DebuggerStepThrough]
+    public static IDisposable Subscribe<T, TState>(this Observable<T> source, TState state, Action<T, TState> onNext, bool riseOnSubscription)
+    {
+        return source.Subscribe(new AnonymousObserver<T, TState>(onNext, Stubs<TState>.HandleException, Stubs<TState>.HandleResult, state), riseOnSubscription);
+    }
+
+    [DebuggerStepThrough]
+    public static IDisposable Subscribe<T, TState>(this Observable<T> source, TState state, Action<T, TState> onNext, Action<Result, TState> onCompleted, bool riseOnSubscription)
+    {
+        return source.Subscribe(new AnonymousObserver<T, TState>(onNext, Stubs<TState>.HandleException, onCompleted, state), riseOnSubscription);
+    }
+
+    [DebuggerStepThrough]
+    public static IDisposable Subscribe<T, TState>(this Observable<T> source, TState state, Action<T, TState> onNext, Action<Exception, TState> onErrorResume, Action<Result, TState> onCompleted, bool riseOnSubscription)
+    {
+        return source.Subscribe(new AnonymousObserver<T, TState>(onNext, onErrorResume, onCompleted, state), riseOnSubscription);
+    }
 }
 
 [DebuggerStepThrough]

src/R3/ReactiveProperty.cs

@@ -189,6 +189,11 @@ public void OnCompleted(Result result)
     }
 
     protected override IDisposable SubscribeCore(Observer<T> observer)
+    {
+        return SubscribeCore(observer, true);
+    }
+
+    protected IDisposable SubscribeCore(Observer<T> observer, bool riseOnSubscription)
     {
         Result? completedResult;
         lock (this)
@@ -210,7 +215,10 @@ protected override IDisposable SubscribeCore(Observer<T> observer)
         }
 
         // raise latest value on subscribe(before add observer to list)
-        observer.OnNext(currentValue);
+        if (riseOnSubscription)
+        {
+            observer.OnNext(currentValue);
+        }
 
         lock (this)
         {
@@ -245,6 +253,11 @@ protected override IDisposable SubscribeCore(Observer<T> observer)
         return Disposable.Empty;
     }
 
+    public IDisposable Subscribe(Observer<T> observer, bool riseOnSubscription = true)
+    {
+        return SubscribeCore(observer, riseOnSubscription);
+    }
+
     void ThrowIfDisposed()
     {
         if (IsDisposed) throw new ObjectDisposedException("");

tests/R3.Tests/ReactivePropertyTest.cs

@@ -229,7 +229,7 @@ public void NodeDisposeCheck()
 
             list1.AssertEqual([1, 10, 20]);
             list2.AssertEqual([1, 10, 20]);
-            list3.AssertEqual([1, 10, 20]);
+            list3.AssertEqual([1, 10]);
             list4.AssertEqual([1]);
             list5.AssertEqual([1, 10, 20]);
         }
@@ -415,4 +415,30 @@ public void RemoveLast()
 [P2]2
 """);
     }
+
+    [Fact]
+    public void SubscribeWithRiseOnSubscription()
+    {
+        var rp = new ReactiveProperty<int>(100);
+        var log = new List<int>();
+
+        rp.Subscribe(new AnonymousObserver<int>(log.Add, _ => { }, _ => { }), riseOnSubscription: true);
+        log.Should().Equal(100);
+
+        rp.Value = 200;
+        log.Should().Equal(100, 200);
+    }
+
+    [Fact]
+    public void SubscribeWithoutRiseOnSubscription()
+    {
+        var rp = new ReactiveProperty<int>(100);
+        var log = new List<int>();
+
+        rp.Subscribe(new AnonymousObserver<int>(log.Add, _ => { }, _ => { }), riseOnSubscription: false);
+        log.Should().BeEmpty();
+
+        rp.Value = 200;
+        log.Should().Equal(200);
+    }
 }