Merge pull request #423 from CesiumGS/unwrapped-shared-futures

Allow a continuation attached to a SharedFuture to return a Future (rather than a normal value)

CHANGES.md

@@ -33,6 +33,7 @@
 ##### Fixes :wrench:
 
 - Fixes a bug where `notifyTileDoneLoading` is not called when encountering Ion responses that can't be parsed.
+- Fixed a bug that prevented a continuation attached to a `SharedFuture` from returning a `Future` itself.
 
 ### v0.11.0 - 2022-01-03
 

CesiumAsync/include/CesiumAsync/Impl/WithTracing.h

@@ -59,7 +59,7 @@ template <typename T> struct WithTracingShared {
       return result;
     };
 #else
-    return Impl::unwrapFuture<Func, T>(std::forward<Func>(f));
+    return Impl::unwrapSharedFuture<Func, T>(std::forward<Func>(f));
 #endif
   }
 
@@ -67,7 +67,7 @@ template <typename T> struct WithTracingShared {
   static auto end([[maybe_unused]] const char* tracingName, Func&& f) {
 #if CESIUM_TRACING_ENABLED
     return [tracingName,
-            f = Impl::unwrapFuture<Func, T>(std::forward<Func>(f)),
+            f = Impl::unwrapSharedFuture<Func, T>(std::forward<Func>(f)),
             CESIUM_TRACE_LAMBDA_CAPTURE_TRACK()](const T& result) mutable {
       CESIUM_TRACE_USE_CAPTURED_TRACK();
       if (tracingName) {
@@ -76,7 +76,7 @@ template <typename T> struct WithTracingShared {
       return f(result);
     };
 #else
-    return Impl::unwrapFuture<Func, T>(std::forward<Func>(f));
+    return Impl::unwrapSharedFuture<Func, T>(std::forward<Func>(f));
 #endif
   }
 };

CesiumAsync/include/CesiumAsync/Impl/unwrapFuture.h

@@ -12,6 +12,10 @@ struct IdentityUnwrapper {
   template <typename Func> static Func unwrap(Func&& f) {
     return std::forward<Func>(f);
   }
+
+  template <typename Func> static Func unwrapShared(Func&& f) {
+    return std::forward<Func>(f);
+  }
 };
 
 template <typename T> struct ParameterizedTaskUnwrapper {
@@ -20,6 +24,11 @@ template <typename T> struct ParameterizedTaskUnwrapper {
       return f(std::move(t))._task;
     };
   }
+
+  template <typename Func> static auto unwrapShared(Func&& f) {
+    return
+        [f = std::forward<Func>(f)](const T& t) mutable { return f(t)._task; };
+  }
 };
 
 struct TaskUnwrapper {
@@ -38,6 +47,16 @@ template <typename Func, typename T> auto unwrapFuture(Func&& f) {
       ParameterizedTaskUnwrapper<T>>::type::unwrap(std::forward<Func>(f));
 }
 
+template <typename Func, typename T> auto unwrapSharedFuture(Func&& f) {
+  return std::conditional<
+      std::is_same<
+          typename ContinuationReturnType<Func, T>::type,
+          typename RemoveFuture<
+              typename ContinuationFutureType<Func, T>::type>::type>::value,
+      IdentityUnwrapper,
+      ParameterizedTaskUnwrapper<T>>::type::unwrapShared(std::forward<Func>(f));
+}
+
 template <typename Func> auto unwrapFuture(Func&& f) {
   return std::conditional<
       std::is_same<
@@ -48,6 +67,10 @@ template <typename Func> auto unwrapFuture(Func&& f) {
       TaskUnwrapper>::type::unwrap(std::forward<Func>(f));
 }
 
+template <typename Func> auto unwrapSharedFuture(Func&& f) {
+  return unwrapFuture(std::forward<Func>(f));
+}
+
 //! @endcond
 // End omitting doxgen warnings for Impl namespace
 } // namespace Impl