feat: add I#vouch

src/main/java/kiss/I.java

@@ -969,11 +969,8 @@ public static <T> Signal<T> http(String request, Class<T> type, HttpClient... cl
      */
     public static <T> Signal<T> http(HttpRequest.Builder request, Class<T> type, HttpClient... client) {
         return new Signal<>((observer, disposer) -> {
-            return disposer.add(I.signal(client)
-                    .to()
-                    .or(I.client)
-                    .sendAsync(request.build(), BodyHandlers.ofInputStream())
-                    .whenComplete((res, e) -> {
+            return disposer
+                    .add(I.vouch(I.client, client).sendAsync(request.build(), BodyHandlers.ofInputStream()).whenComplete((res, e) -> {
                         if (e == null) try {
                             if (res.statusCode() < 400) {
                                 InputStream in = res.body();
@@ -1027,9 +1024,7 @@ public static Signal<String> http(String uri, Consumer<WebSocket> open, HttpClie
             sub.next = open;
             sub.o = new StringBuilder();
 
-            return disposer.add(I.signal(client)
-                    .to()
-                    .or(I.client)
+            return disposer.add(I.vouch(I.client, client)
                     .newWebSocketBuilder()
                     .connectTimeout(Duration.ofSeconds(15))
                     .buildAsync(URI.create(uri), sub)
@@ -2021,7 +2016,7 @@ public static Signal<Long> schedule(long delayTime, long intervalTime, TimeUnit
             Runnable task = I.wiseC(observer).bindLast(null);
             Future future;
 
-            ScheduledExecutorService exe = scheduler == null || scheduler.length == 0 || scheduler[0] == null ? I.Jobs : scheduler[0];
+            ScheduledExecutorService exe = vouch(Jobs, scheduler);
 
             if (intervalTime <= 0) {
                 future = delayTime <= 0 ? CompletableFuture.runAsync(task, Runnable::run) : exe.schedule(task, delayTime, unit);
@@ -2235,6 +2230,19 @@ public static Class type(String fqcn) {
         }
     }
 
+    /**
+     * Obtains the last non-null value from the specified array. If there is no suitable value in
+     * the array or the array itself, the default value is retrieved.
+     * 
+     * @param <T> A type of value.
+     * @param defaults A default value.
+     * @param values A candidate of values.
+     * @return A suitable value.
+     */
+    public static <T> T vouch(T defaults, T... values) {
+        return I.signal(values).skipNull().to().or(defaults);
+    }
+
     /**
      * Write {@link java.lang.System.Logger.Level#WARNING} log.
      * 

src/main/java/kiss/Signal.java

@@ -1822,31 +1822,8 @@ public Signal<Boolean> isTerminated() {
      * @param function A mapper function.
      * @return {ChainableAPI}
      */
-    public <R> Signal<R> joinAll(WiseFunction<V, R> function) {
-        return joinAll(function, null);
-    }
-
-    /**
-     * Returns a new {@link Signal} that invokes the mapper action in parallel thread and waits all
-     * of them until all actions are completed.
-     *
-     * @param function A mapper function.
-     * @return {ChainableAPI}
-     */
-    public <R> Signal<R> joinAll(WiseFunction<V, R> function, ExecutorService executor) {
-        return map(function::bind).buffer()
-                .flatIterable(v -> I.signal((executor == null ? I.Jobs : executor).invokeAll(v)).map(Future::get).toList());
-    }
-
-    /**
-     * Returns a new {@link Signal} that invokes the mapper action in parallel thread and waits
-     * until any single action is completed. All other actions will be cancelled.
-     * 
-     * @param function A mapper function.
-     * @return {ChainableAPI}
-     */
-    public <R> Signal<R> joinAny(WiseFunction<V, R> function) {
-        return joinAny(function, null);
+    public <R> Signal<R> joinAll(WiseFunction<V, R> function, ExecutorService... executor) {
+        return map(function::bind).buffer().flatIterable(v -> I.signal(I.vouch(I.Jobs, executor).invokeAll(v)).map(Future::get).toList());
     }
 
     /**
@@ -1856,8 +1833,9 @@ public <R> Signal<R> joinAny(WiseFunction<V, R> function) {
      * @param function A mapper function.
      * @return {ChainableAPI}
      */
-    public <R> Signal<R> joinAny(WiseFunction<V, R> function, ExecutorService executor) {
-        return map(function::bind).buffer().map((executor == null ? I.Jobs : executor)::invokeAny);
+    @SuppressWarnings("resource")
+    public <R> Signal<R> joinAny(WiseFunction<V, R> function, ExecutorService... executor) {
+        return map(function::bind).buffer().map(I.vouch(I.Jobs, executor)::invokeAny);
     }
 
     /**
@@ -2116,20 +2094,6 @@ public <O> Signal<O> plug(Function<Signal<V>, Signal<O>> plug) {
         return plug.apply(this);
     }
 
-    /**
-     * <p>
-     * Returns an {@link Signal} that emits items based on applying a function that you supply to
-     * each item emitted by the source {@link Signal}, where that function returns an {@link Signal}
-     * , and then merging those resulting {@link Signal} and emitting the results of this merger.
-     * </p>
-     * 
-     * @param recurse A mapper function to enumerate values recursively.
-     * @return {ChainableAPI}
-     */
-    public Signal<V> recurse(WiseFunction<V, V> recurse) {
-        return recurse(recurse, Runnable::run);
-    }
-
     /**
      * <p>
      * Returns an {@link Signal} that emits items based on applying a function that you supply to
@@ -2141,24 +2105,10 @@ public Signal<V> recurse(WiseFunction<V, V> recurse) {
      * @param executor An execution context.
      * @return {ChainableAPI}
      */
-    public Signal<V> recurse(WiseFunction<V, V> recurse, Executor executor) {
+    public Signal<V> recurse(WiseFunction<V, V> recurse, Executor... executor) {
         return recurseMap(e -> e.map(recurse), executor);
     }
 
-    /**
-     * <p>
-     * Returns an {@link Signal} that emits items based on applying a function that you supply to
-     * each item emitted by the source {@link Signal}, where that function returns an {@link Signal}
-     * , and then merging those resulting {@link Signal} and emitting the results of this merger.
-     * </p>
-     * 
-     * @param recurse A mapper function to enumerate values recursively.
-     * @return {ChainableAPI}
-     */
-    public Signal<V> recurseMap(WiseFunction<Signal<V>, Signal<V>> recurse) {
-        return recurseMap(recurse, Runnable::run);
-    }
-
     /**
      * <p>
      * Returns an {@link Signal} that emits items based on applying a function that you supply to
@@ -2170,10 +2120,10 @@ public Signal<V> recurseMap(WiseFunction<Signal<V>, Signal<V>> recurse) {
      * @param executor An execution context.
      * @return {ChainableAPI}
      */
-    public Signal<V> recurseMap(WiseFunction<Signal<V>, Signal<V>> recurse, Executor executor) {
+    public Signal<V> recurseMap(WiseFunction<Signal<V>, Signal<V>> recurse, Executor... executor) {
         // DON'T use the recursive call, it will throw StackOverflowError.
         return flatMap(init -> new Signal<>((observer, disposer) -> {
-            (executor == null ? I.Jobs : executor).execute(() -> {
+            I.vouch(Runnable::run, executor).execute(() -> {
                 try {
                     LinkedList<V> values = new LinkedList(); // LinkedList accepts null
                     LinkedTransferQueue<Signal<V>> signal = new LinkedTransferQueue();
@@ -3514,42 +3464,4 @@ private <T> Signal<T> signal(Predicate<? super V> emitCondition, T emitOutput, b
             }, sub, false);
         });
     }
-
-    // /**
-    // * <p>
-    // * Append the current time to each event.
-    // * </p>
-    // *
-    // * @return Chainable API.
-    // */
-    // public Signal<Ⅱ<V, Instant>> timeStamp() {
-    // return map(value -> I.pair(value, Instant.now()));
-    // }
-    //
-    // /**
-    // * <p>
-    // * Append {@link Duration} between the current value and the previous value.
-    // * </p>
-    // *
-    // * @return Chainable API.
-    // */
-    // public Signal<Ⅱ<V, Duration>> timeInterval() {
-    // return timeStamp().map((Ⅱ) null, (prev, now) -> I.pair(now.ⅰ, Duration.between(prev == null ?
-    // now.ⅱ : prev.ⅱ, now.ⅱ)));
-    // }
-    //
-    // /**
-    // * <p>
-    // * Append {@link Duration} between the current value and the first value.
-    // * </p>
-    // *
-    // * @return Chainable API.
-    // */
-    // public Signal<Ⅱ<V, Duration>> timeElapsed() {
-    // return map(Variable::<Instant> empty, (context, value) -> {
-    // Instant prev = context.let(Instant::now);
-    //
-    // return I.pair(value, prev == null ? Duration.ZERO : Duration.between(prev, Instant.now()));
-    // });
-    // }
 }

src/test/java/kiss/core/VouchTest.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2024 Nameless Production Committee
+ *
+ * Licensed under the MIT License (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *          http://opensource.org/licenses/mit-license.php
+ */
+package kiss.core;
+
+import org.junit.jupiter.api.Test;
+
+import kiss.I;
+
+class VouchTest {
+
+    @Test
+    void vouch() {
+        assert I.vouch("DEF", "A").equals("A");
+        assert I.vouch("DEF", "A", "B", "C").equals("C");
+        assert I.vouch("DEF", "A", "B", null).equals("B");
+        assert I.vouch("DEF", "A", null, "C").equals("C");
+    }
+
+    @Test
+    void empty() {
+        assert I.vouch("DEF", new String[0]).equals("DEF");
+    }
+
+    @Test
+    void nullValues() {
+        assert I.vouch("DEF", (String[]) null).equals("DEF");
+    }
+
+    @Test
+    void nullDefault() {
+        assert I.vouch(null, (String[]) null) == null;
+    }
+}