folly | Inline Future constructors to workaround MSVC bug (#1212)

Summary:
Pull Request resolved: https://github.com/facebook/folly/pull/1212

MSVC has a bug and can't match definitions of some of the constructors to the corresponding declarations in a class body. This diff workarounds the bug by inlining constructors.

Reviewed By: LeeHowes

Differential Revision: D17119718

fbshipit-source-id: eb7a9d4916b962c718d047eb0ee7fa4a9761776e

folly/futures/Future-inl.h

@@ -206,14 +206,6 @@ FutureBase<T>::FutureBase(
     typename std::enable_if<std::is_same<Unit, T2>::value>::type*)
     : core_(Core::make(Try<T>(T()))) {}
 
-template <class T>
-template <
-    class... Args,
-    typename std::enable_if<std::is_constructible<T, Args&&...>::value, int>::
-        type>
-FutureBase<T>::FutureBase(in_place_t, Args&&... args)
-    : core_(Core::make(in_place, std::forward<Args>(args)...)) {}
-
 template <class T>
 void FutureBase<T>::assign(FutureBase<T>&& other) noexcept {
   detach();
@@ -898,42 +890,6 @@ Future<T>& Future<T>::operator=(Future<T>&& other) noexcept {
   return *this;
 }
 
-template <class T>
-template <
-    class T2,
-    typename std::enable_if<
-        !std::is_same<T, typename std::decay<T2>::type>::value &&
-            std::is_constructible<T, T2&&>::value &&
-            std::is_convertible<T2&&, T>::value,
-        int>::type>
-Future<T>::Future(Future<T2>&& other)
-    : Future(
-          std::move(other).thenValue([](T2&& v) { return T(std::move(v)); })) {}
-
-template <class T>
-template <
-    class T2,
-    typename std::enable_if<
-        !std::is_same<T, typename std::decay<T2>::type>::value &&
-            std::is_constructible<T, T2&&>::value &&
-            !std::is_convertible<T2&&, T>::value,
-        int>::type>
-Future<T>::Future(Future<T2>&& other)
-    : Future(
-          std::move(other).thenValue([](T2&& v) { return T(std::move(v)); })) {}
-
-template <class T>
-template <
-    class T2,
-    typename std::enable_if<
-        !std::is_same<T, typename std::decay<T2>::type>::value &&
-            std::is_constructible<T, T2&&>::value,
-        int>::type>
-Future<T>& Future<T>::operator=(Future<T2>&& other) {
-  return operator=(
-      std::move(other).thenValue([](T2&& v) { return T(std::move(v)); }));
-}
-
 // unwrap
 
 template <class T>

folly/futures/Future.h

@@ -147,7 +147,8 @@ class FutureBase {
       class... Args,
       typename std::enable_if<std::is_constructible<T, Args&&...>::value, int>::
           type = 0>
-  explicit FutureBase(in_place_t, Args&&... args);
+  explicit FutureBase(in_place_t, Args&&... args)
+      : core_(Core::make(in_place, std::forward<Args>(args)...)) {}
 
   FutureBase(FutureBase<T> const&) = delete;
   FutureBase(SemiFuture<T>&&) noexcept;
@@ -998,7 +999,10 @@ class Future : private futures::detail::FutureBase<T> {
               std::is_constructible<T, T2&&>::value &&
               std::is_convertible<T2&&, T>::value,
           int>::type = 0>
-  /* implicit */ Future(Future<T2>&&);
+  /* implicit */ Future(Future<T2>&& other)
+      : Future(std::move(other).thenValue(
+            [](T2&& v) { return T(std::move(v)); })) {}
+
   template <
       class T2,
       typename std::enable_if<
@@ -1006,14 +1010,20 @@ class Future : private futures::detail::FutureBase<T> {
               std::is_constructible<T, T2&&>::value &&
               !std::is_convertible<T2&&, T>::value,
           int>::type = 0>
-  explicit Future(Future<T2>&&);
+  explicit Future(Future<T2>&& other)
+      : Future(std::move(other).thenValue(
+            [](T2&& v) { return T(std::move(v)); })) {}
+
   template <
       class T2,
       typename std::enable_if<
           !std::is_same<T, typename std::decay<T2>::type>::value &&
               std::is_constructible<T, T2&&>::value,
           int>::type = 0>
-  Future& operator=(Future<T2>&&);
+  Future& operator=(Future<T2>&& other) {
+    return operator=(
+        std::move(other).thenValue([](T2&& v) { return T(std::move(v)); }));
+  }
 
   using Base::cancel;
   using Base::hasException;