Implement CompletionStage toCompletableFuture

Author: cosineblast

src/manifold/deferred.clj

@@ -69,7 +69,9 @@
          then-compose then-compose-async
 
          then-handle then-handle-async
-         then-exceptionally)
+         then-exceptionally
+
+         to-completable-future)
 
 ;; The potemkin abstract type for
 ;; implementations such as CompletionStage
@@ -153,7 +155,10 @@
     (then-handle-async this operator executor))
 
   (exceptionally [this operator]
-    (then-exceptionally this operator)))
+    (then-exceptionally this operator))
+
+  (toCompletableFuture [this]
+    (to-completable-future this)))
 
 (definline realized?
   "Returns true if the manifold deferred is realized."
@@ -1625,6 +1630,17 @@
   (assert-some operator)
   (catch this #(.apply operator %)))
 
+(defn- to-completable-future [this]
+
+  (let [result (java.util.concurrent.CompletableFuture.)]
+
+    (on-realized this
+                 #(.complete result %)
+                 #(.completeExceptionally result %))
+
+    result
+    ))
+
 ;;;
 
 (alter-meta! #'->Deferred assoc :private true)

test/manifold/deferred_stage_test.clj

@@ -454,3 +454,28 @@
 
       (is (thrown? RuntimeException @d1))
       (is (= 2 @d2)))))
+
+(deftest test-to-completable-future
+  (testing ".toCompletableFuture success"
+    (let [base ^CompletionStage (d/deferred)
+          target ^CompletableFuture (.toCompletableFuture base)]
+
+      (is (not (.isDone target)))
+
+      (d/success! base 10)
+
+      (is (.isDone target))
+
+      (is (= 10 (.get target)))))
+
+  (testing ".toCompletableFuture error"
+    (let [base ^CompletionStage (d/deferred)
+          target ^CompletableFuture (.toCompletableFuture base)]
+
+      (is (not (.isDone target)))
+
+      (d/error! base (RuntimeException.))
+
+      (is (.isDone target))
+
+      (is (thrown? RuntimeException (.getNow target nil))))))