Defer

sandbox/ConsoleApp1/Program.cs

@@ -30,7 +30,7 @@
 
 var range = System.Reactive.Linq.Observable.Range(1, 10);
 
-
+System.Reactive.Linq.Observable.Defer(
 
 // range.TakeLast(
 

src/R3/Factories/Defer.cs

@@ -0,0 +1,29 @@
+namespace R3;
+
+public static partial class Observable
+{
+    public static Observable<T> Defer<T>(Func<Observable<T>> observableFactory)
+    {
+        return new Defer<T>(observableFactory);
+    }
+}
+
+
+internal sealed class Defer<T>(Func<Observable<T>> observableFactory) : Observable<T>
+{
+    protected override IDisposable SubscribeCore(Observer<T> observer)
+    {
+        var observable = default(Observable<T>);
+        try
+        {
+            observable = observableFactory();
+        }
+        catch (Exception ex)
+        {
+            observer.OnCompleted(ex); // when failed, return Completed(Error)
+            return Disposable.Empty;
+        }
+
+        return observable.Subscribe(observer);
+    }
+}

src/R3/Factories/ReturnOnCompleted.cs

@@ -4,7 +4,14 @@ public static partial class Observable
 {
     public static Observable<T> ReturnOnCompleted<T>(Result result)
     {
-        return new ImmediateScheduleReturnOnCompleted<T>(result); // immediate
+        if (result.IsSuccess)
+        {
+            return ImmediateScheduleReturnOnCompletedSuccess<T>.Instance; // singleton
+        }
+        else
+        {
+            return new ImmediateScheduleReturnOnCompleted<T>(result); // immediate
+        }
     }
 
     public static Observable<T> ReturnOnCompleted<T>(Result result, TimeProvider timeProvider)
@@ -26,6 +33,22 @@ public static Observable<T> ReturnOnCompleted<T>(Result result, TimeSpan dueTime
     }
 }
 
+internal class ImmediateScheduleReturnOnCompletedSuccess<T> : Observable<T>
+{
+    public static readonly Observable<T> Instance = new ImmediateScheduleReturnOnCompletedSuccess<T>();
+
+    ImmediateScheduleReturnOnCompletedSuccess()
+    {
+
+    }
+
+    protected override IDisposable SubscribeCore(Observer<T> observer)
+    {
+        observer.OnCompleted(Result.Success);
+        return Disposable.Empty;
+    }
+}
+
 internal class ImmediateScheduleReturnOnCompleted<T>(Result result) : Observable<T>
 {
     protected override IDisposable SubscribeCore(Observer<T> observer)

src/R3/Factories/ToObservable.cs

@@ -2,6 +2,8 @@
 
 public static partial class Observable
 {
+    // TODO: not tested.
+
     public static Observable<T> ToObservable<T>(this Task<T> task)
     {
         return new TaskToObservable<T>(task);

src/R3/Factories/_EventFactory.cs

@@ -1,23 +1,16 @@
-using R3.Internal;
-
-namespace R3;
+namespace R3;
 
 public static partial class Observable
 {
     // TODO: this is working space, will remove this file after complete.
 
     // TODO: Defer, DeferAsync, Start, Using, Create
-    // ToObservable(ToEvent)
-
 
 
+    // ToObservable(ToEvent)
     // ToAsyncEnumerable?
-
     // AsObservable
     // AsSingleUnitObservable
-
     // AsUnitObservable
     // AsUniResult
-    // AsNeverComplete
 }
-

tests/R3.Tests/FactoryTests/DeferTest.cs

@@ -0,0 +1,23 @@
+namespace R3.Tests.FactoryTests;
+
+public class DeferTest
+{
+    [Fact]
+    public void Test()
+    {
+        var called = false;
+        var def = Observable.Defer(() =>
+        {
+            called = true;
+            return Observable.Range(1, 10);
+        });
+
+        called.Should().BeFalse();
+
+        var list = def.ToLiveList();
+
+        called.Should().BeTrue();
+
+        list.AssertEqual([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
+    }
+}