Adding bounded generics in Promise/Promises/DependentPromise

Author: vsilaev

src/main/java/net/tascalate/concurrent/DependentPromise.java

@@ -129,7 +129,7 @@ public T getNow(T valueIfAbsent) {
         return completionStage.getNow(valueIfAbsent);
     }
 
-    public T getNow(Supplier<T> valueIfAbsent) {
+    public T getNow(Supplier<? extends T> valueIfAbsent) {
         return completionStage.getNow(valueIfAbsent);
     }
 
@@ -203,31 +203,31 @@ public DependentPromise<T> onTimeout(T value, Duration duration, boolean cancelO
         return onTimeout(() -> value, duration, enlistOrigin); 
     }
 
-    public DependentPromise<T> onTimeout(Supplier<T> supplier, long timeout, TimeUnit unit) {
+    public DependentPromise<T> onTimeout(Supplier<? extends T> supplier, long timeout, TimeUnit unit) {
         return onTimeout(supplier, timeout, unit, true);
     }
 
-    public DependentPromise<T> onTimeout(Supplier<T> supplier, long timeout, TimeUnit unit, boolean cancelOnTimeout) {
+    public DependentPromise<T> onTimeout(Supplier<? extends T> supplier, long timeout, TimeUnit unit, boolean cancelOnTimeout) {
         return onTimeout(supplier, Promises.toDuration(timeout, unit), false);
     }
 
-    public DependentPromise<T> onTimeout(Supplier<T> supplier, long timeout, TimeUnit unit, boolean cancelOnTimeout, boolean enlistOrigin) {
+    public DependentPromise<T> onTimeout(Supplier<? extends T> supplier, long timeout, TimeUnit unit, boolean cancelOnTimeout, boolean enlistOrigin) {
         return onTimeout(supplier, Promises.toDuration(timeout, unit), enlistOrigin);
     }
 
-    public DependentPromise<T> onTimeout(Supplier<T> supplier, Duration duration) {
+    public DependentPromise<T> onTimeout(Supplier<? extends T> supplier, Duration duration) {
         return onTimeout(supplier, duration, true);
     }
 
-    public DependentPromise<T> onTimeout(Supplier<T> supplier, Duration duration, boolean cancelOnTimeout) {
+    public DependentPromise<T> onTimeout(Supplier<? extends T> supplier, Duration duration, boolean cancelOnTimeout) {
         return onTimeout(supplier, duration, cancelOnTimeout, false);
     }
 
-    public DependentPromise<T> onTimeout(Supplier<T> supplier, Duration duration, boolean cancelOnTimeout, boolean enlistOrigin) {
-        Function<T, Supplier<T>> valueToSupplier = v -> () -> v;
+    public DependentPromise<T> onTimeout(Supplier<? extends T> supplier, Duration duration, boolean cancelOnTimeout, boolean enlistOrigin) {
+        Function<T, Supplier<? extends T>> valueToSupplier = v -> () -> v;
 
         // timeout converted to supplier
-        Promise<Supplier<T>> onTimeout = Promises
+        Promise<Supplier<? extends T>> onTimeout = Promises
             .delay(duration)
             .dependent()
             .thenApply(d -> supplier, true);

src/main/java/net/tascalate/concurrent/Promise.java

@@ -45,7 +45,7 @@ default public T getNow(T valueIfAbsent) {
         return getNow(() -> valueIfAbsent);
     }
 
-    default public T getNow(Supplier<T> valueIfAbsent) {
+    default public T getNow(Supplier<? extends T> valueIfAbsent) {
         if (isDone()) {
             try {
                 return get();
@@ -98,23 +98,23 @@ default Promise<T> onTimeout(T value, Duration duration, boolean cancelOnTimeout
         return onTimeout(() -> value, duration, cancelOnTimeout);
     }
 
-    default Promise<T> onTimeout(Supplier<T> supplier, long timeout, TimeUnit unit) {
+    default Promise<T> onTimeout(Supplier<? extends T> supplier, long timeout, TimeUnit unit) {
         return onTimeout(supplier, timeout, unit, true);
     }
 
-    default Promise<T> onTimeout(Supplier<T> supplier, long timeout, TimeUnit unit, boolean cancelOnTimeout) {
+    default Promise<T> onTimeout(Supplier<? extends T> supplier, long timeout, TimeUnit unit, boolean cancelOnTimeout) {
         return onTimeout(supplier, Promises.toDuration(timeout, unit), cancelOnTimeout);
     }
 
-    default Promise<T> onTimeout(Supplier<T> supplier, Duration duration) {
+    default Promise<T> onTimeout(Supplier<? extends T> supplier, Duration duration) {
         return onTimeout(supplier, duration, true);
     }
 
-    default Promise<T> onTimeout(Supplier<T> supplier, Duration duration, boolean cancelOnTimeout) {
-        Function<T, Supplier<T>> valueToSupplier = v -> () -> v;
+    default Promise<T> onTimeout(Supplier<? extends T> supplier, Duration duration, boolean cancelOnTimeout) {
+        Function<T, Supplier<? extends T>> valueToSupplier = v -> () -> v;
 
         // timeout converted to supplier
-        Promise<Supplier<T>> onTimeout = Promises
+        Promise<Supplier<? extends T>> onTimeout = Promises
             .delay(duration)
             .dependent()
             .thenApply(d -> supplier, true);

src/main/java/net/tascalate/concurrent/Promises.java

@@ -99,7 +99,7 @@ public static <T> Promise<T> from(CompletionStage<T> stage) {
         return result;
     }
 
-    static <T, R> Promise<R> from(CompletionStage<T> stage, 
+    static <T, R> Promise<R> from(CompletionStage<? extends T> stage, 
                                   Function<? super T, ? extends R> resultConverter,
                                   Function<? super Throwable, ? extends Throwable> errorConverter) {
 
@@ -111,13 +111,13 @@ static <T, R> Promise<R> from(CompletionStage<T> stage,
         return result;
     }
 
-    public static <T> Promise<T> task(CompletionStage<T> stage, Executor executor) {
+    public static <T> Promise<T> task(CompletionStage<? extends T> stage, Executor executor) {
         return CompletableTask.asyncOn(executor)
                .dependent()
                .thenCombineAsync(stage, (u, v) -> v, PromiseOrigin.PARAM_ONLY);
     }
 
-    private static <T, R> CompletablePromise<R> createLinkedPromise(CompletionStage<T> stage) {
+    private static <T, R> CompletablePromise<R> createLinkedPromise(CompletionStage<? extends T> stage) {
         return new CompletablePromise<R>() {
             @Override
             public boolean cancel(boolean mayInterruptIfRunning) {