Let Future handle throwing FutureNotReady

Summary: [Folly] Let `Future` handle throwing `FutureNotReady`, since it is logically the thing that knows about specific exceptions in its contract.

Reviewed By: LeeHowes

Differential Revision: D7964855

fbshipit-source-id: 49f3220a6a41ebe87f577814c0940e00497092c0

folly/futures/Future-inl.h

@@ -191,22 +191,22 @@ T const&& FutureBase<T>::value() const&& {
 
 template <class T>
 Try<T>& FutureBase<T>::result() & {
-  return getCore().getTry();
+  return getCoreTryChecked();
 }
 
 template <class T>
 Try<T> const& FutureBase<T>::result() const& {
-  return getCore().getTry();
+  return getCoreTryChecked();
 }
 
 template <class T>
 Try<T>&& FutureBase<T>::result() && {
-  return std::move(getCore().getTry());
+  return std::move(getCoreTryChecked());
 }
 
 template <class T>
 Try<T> const&& FutureBase<T>::result() const&& {
-  return std::move(getCore().getTry());
+  return std::move(getCoreTryChecked());
 }
 
 template <class T>

folly/futures/Future.h

@@ -188,6 +188,22 @@ class FutureBase {
     return *self.core_;
   }
 
+  Try<T>& getCoreTryChecked() {
+    return getCoreTryChecked(*this);
+  }
+  Try<T> const& getCoreTryChecked() const {
+    return getCoreTryChecked(*this);
+  }
+
+  template <typename Self>
+  static decltype(auto) getCoreTryChecked(Self& self) {
+    auto& core = self.getCore();
+    if (!core.hasResult()) {
+      throwFutureNotReady();
+    }
+    return core.getTry();
+  }
+
   // shared core state object
   // usually you should use `getCore()` instead of directly accessing `core_`.
   corePtr core_;

folly/futures/detail/Core.h

@@ -28,7 +28,6 @@
 #include <folly/ScopeGuard.h>
 #include <folly/Try.h>
 #include <folly/Utility.h>
-#include <folly/futures/FutureException.h>
 #include <folly/futures/detail/FSM.h>
 #include <folly/lang/Assume.h>
 #include <folly/lang/Exception.h>
@@ -401,11 +400,8 @@ class Core final {
 
   template <typename Self>
   static decltype(auto) getTryImpl(Self& self) {
-    if (self.ready()) {
-      return *self.result_;
-    } else {
-      throwFutureNotReady();
-    }
+    assume(self.result_.has_value());
+    return self.result_.value();
   }
 
   folly::Function<void(Try<T>&&)> callback_;