Backport std::apply and remove folly::applyTuple

Summary:
Add a backport of `std::apply` with a similar implementation that makes it easy
to reason about.  Also implement `applyTuple` in terms of `apply`, `invoke` and
`tuple_cat`

The implementation of `apply` has been taken straight from the standard,
reducing chances of churn in incompatible assumptions (if any).  Note that the
definition and declaration of `apply` has been changed from the way it is
specified in the standard for better SFINAE compatibility, if needed, will
followup with a paper proposing the same change in the standard

Reviewed By: spacedentist

Differential Revision: D8248199

fbshipit-source-id: e3e76193a30b1599eca3fe986a33f61addad7a59

folly/functional/ApplyTuple.h

@@ -14,17 +14,6 @@
  * limitations under the License.
  */
 
-/*
- * Defines a function folly::applyTuple, which takes a function and a
- * std::tuple of arguments and calls the function with those
- * arguments.
- *
- * Example:
- *
- *    int x = folly::applyTuple(std::plus<int>(), std::make_tuple(12, 12));
- *    ASSERT(x == 24);
- */
-
 #pragma once
 
 #include <functional>
@@ -39,70 +28,22 @@ namespace folly {
 //////////////////////////////////////////////////////////////////////
 
 namespace detail {
-namespace apply_tuple {
-
-inline constexpr std::size_t sum() {
-  return 0;
-}
-template <typename... Args>
-inline constexpr std::size_t sum(std::size_t v1, Args... vs) {
-  return v1 + sum(vs...);
-}
-
-template <typename... Tuples>
-struct TupleSizeSum {
-  static constexpr auto value = sum(std::tuple_size<Tuples>::value...);
-};
-
-template <typename... Tuples>
-using MakeIndexSequenceFromTuple = folly::make_index_sequence<
-    TupleSizeSum<typename std::decay<Tuples>::type...>::value>;
-
-template <class F, class Tuple, std::size_t... Indexes>
-inline constexpr auto call(F&& f, Tuple&& t, folly::index_sequence<Indexes...>)
-    -> decltype(invoke(
-        std::forward<F>(f),
-        std::get<Indexes>(std::forward<Tuple>(t))...)) {
-  return invoke(
-      std::forward<F>(f), std::get<Indexes>(std::forward<Tuple>(t))...);
+template <class F, class T, std::size_t... I>
+constexpr decltype(auto) applyImpl(F&& f, T&& t, folly::index_sequence<I...>) {
+  return invoke(std::forward<F>(f), std::get<I>(std::forward<T>(t))...);
 }
-
-template <class Tuple, std::size_t... Indexes>
-inline constexpr auto forwardTuple(Tuple&& t, folly::index_sequence<Indexes...>)
-    -> decltype(
-        std::forward_as_tuple(std::get<Indexes>(std::forward<Tuple>(t))...)) {
-  return std::forward_as_tuple(std::get<Indexes>(std::forward<Tuple>(t))...);
-}
-
-} // namespace apply_tuple
 } // namespace detail
 
 //////////////////////////////////////////////////////////////////////
 
-/**
- * Invoke a callable object with a set of arguments passed as a tuple, or a
- *     series of tuples
- *
- * Example: the following lines are equivalent
- *     func(1, 2, 3, "foo");
- *     applyTuple(func, std::make_tuple(1, 2, 3, "foo"));
- *     applyTuple(func, std::make_tuple(1, 2), std::make_tuple(3, "foo"));
- */
-
-template <class F, class... Tuples>
-inline constexpr auto applyTuple(F&& f, Tuples&&... t)
-    -> decltype(detail::apply_tuple::call(
-        std::forward<F>(f),
-        std::tuple_cat(detail::apply_tuple::forwardTuple(
-            std::forward<Tuples>(t),
-            detail::apply_tuple::MakeIndexSequenceFromTuple<Tuples>{})...),
-        detail::apply_tuple::MakeIndexSequenceFromTuple<Tuples...>{})) {
-  return detail::apply_tuple::call(
-      std::forward<F>(f),
-      std::tuple_cat(detail::apply_tuple::forwardTuple(
-          std::forward<Tuples>(t),
-          detail::apply_tuple::MakeIndexSequenceFromTuple<Tuples>{})...),
-      detail::apply_tuple::MakeIndexSequenceFromTuple<Tuples...>{});
+//  mimic: std::apply, C++17
+template <typename F, typename Tuple>
+constexpr decltype(auto) apply(F&& func, Tuple&& tuple) {
+  constexpr auto size = std::tuple_size<std::remove_reference_t<Tuple>>::value;
+  return detail::applyImpl(
+      std::forward<F>(func),
+      std::forward<Tuple>(tuple),
+      folly::make_index_sequence<size>{});
 }
 
 namespace detail {
@@ -116,8 +57,8 @@ class Uncurry {
 
   template <class Tuple>
   auto operator()(Tuple&& tuple) const
-      -> decltype(applyTuple(std::declval<F>(), std::forward<Tuple>(tuple))) {
-    return applyTuple(func_, std::forward<Tuple>(tuple));
+      -> decltype(apply(std::declval<F>(), std::forward<Tuple>(tuple))) {
+    return apply(func_, std::forward<Tuple>(tuple));
   }
 
  private:
@@ -173,8 +114,7 @@ struct Construct {
 //  mimic: std::make_from_tuple, C++17
 template <class T, class Tuple>
 constexpr T make_from_tuple(Tuple&& t) {
-  return applyTuple(
-      detail::apply_tuple::Construct<T>(), std::forward<Tuple>(t));
+  return apply(detail::apply_tuple::Construct<T>(), std::forward<Tuple>(t));
 }
 
 #endif

folly/functional/Partial.h

@@ -16,7 +16,11 @@
 
 #pragma once
 
-#include <folly/functional/ApplyTuple.h>
+#include <folly/Utility.h>
+#include <folly/functional/Invoke.h>
+
+#include <tuple>
+#include <utility>
 
 namespace folly {
 
@@ -29,9 +33,19 @@ struct PartialConstructFromCallable {};
 
 template <typename F, typename Tuple>
 class Partial {
- private:
-  F f_;
-  Tuple stored_args_;
+  using Indexes = make_index_sequence<std::tuple_size<Tuple>{}>;
+
+  template <typename Self, std::size_t... I, typename... Args>
+  static auto invokeForward(Self&& self, index_sequence<I...>, Args&&... args)
+      -> decltype(invoke(
+          std::declval<Self>().f_,
+          std::get<I>(std::declval<Self>().stored_args_)...,
+          std::declval<Args>()...)) {
+    return invoke(
+        std::forward<Self>(self).f_,
+        std::get<I>(std::forward<Self>(self).stored_args_)...,
+        std::forward<Args>(args)...);
+  }
 
  public:
   template <typename Callable, typename... Args>
@@ -40,37 +54,40 @@ class Partial {
         stored_args_(std::forward<Args>(args)...) {}
 
   template <typename... CArgs>
-  auto operator()(CArgs&&... cargs) & -> decltype(applyTuple(
-      static_cast<F&>(f_),
-      static_cast<Tuple&>(stored_args_),
-      std::forward_as_tuple(std::forward<CArgs>(cargs)...))) {
-    return applyTuple(
-        static_cast<F&>(f_),
-        static_cast<Tuple&>(stored_args_),
-        std::forward_as_tuple(std::forward<CArgs>(cargs)...));
+  auto operator()(CArgs&&... cargs) & -> decltype(invokeForward(
+      std::declval<Partial&>(),
+      Indexes{},
+      std::declval<CArgs>()...)) {
+    return invokeForward(*this, Indexes{}, std::forward<CArgs>(cargs)...);
   }
-
   template <typename... CArgs>
-  auto operator()(CArgs&&... cargs) const& -> decltype(applyTuple(
-      static_cast<F const&>(f_),
-      static_cast<Tuple const&>(stored_args_),
-      std::forward_as_tuple(std::forward<CArgs>(cargs)...))) {
-    return applyTuple(
-        static_cast<F const&>(f_),
-        static_cast<Tuple const&>(stored_args_),
-        std::forward_as_tuple(std::forward<CArgs>(cargs)...));
+  auto operator()(CArgs&&... cargs) const& -> decltype(invokeForward(
+      std::declval<const Partial&>(),
+      Indexes{},
+      std::declval<CArgs>()...)) {
+    return invokeForward(*this, Indexes{}, std::forward<CArgs>(cargs)...);
   }
-
-  template <typename... CArgs>
-  auto operator()(CArgs&&... cargs) && -> decltype(applyTuple(
-      static_cast<F&&>(f_),
-      static_cast<Tuple&&>(stored_args_),
-      std::forward_as_tuple(std::forward<CArgs>(cargs)...))) {
-    return applyTuple(
-        static_cast<F&&>(f_),
-        static_cast<Tuple&&>(stored_args_),
-        std::forward_as_tuple(std::forward<CArgs>(cargs)...));
+  template <typename... As>
+  auto operator()(As&&... a) && -> decltype(invokeForward(
+      std::declval<Partial&&>(),
+      Indexes{},
+      std::declval<As>()...)) {
+    return invokeForward(std::move(*this), Indexes{}, std::forward<As>(a)...);
   }
+  template <typename... As>
+  auto operator()(As&&... as) const&& -> decltype(invokeForward(
+      std::declval<const Partial&&>(),
+      Indexes{},
+      std::declval<As>()...)) {
+    return invokeForward(std::move(*this), Indexes{}, std::forward<As>(as)...);
+  }
+
+ private:
+  // the stored callable
+  F f_;
+  // the stored arguments, these will be forwarded along with the actual
+  // argumnets to the callable above
+  Tuple stored_args_;
 };
 
 } // namespace partial

folly/functional/test/ApplyTupleTest.cpp

@@ -94,7 +94,7 @@ struct GuardObj : GuardObjBase {
   {}
 
   ~GuardObj() {
-    folly::applyTuple(f_, args_);
+    folly::apply(f_, args_);
   }
 
   GuardObj(const GuardObj&) = delete;
@@ -128,20 +128,19 @@ void move_only_func(Mover&&) {}
 TEST(ApplyTuple, Test) {
   auto argsTuple = std::make_tuple(1, 2, 3.0);
   auto func2 = func;
-  folly::applyTuple(func2, argsTuple);
-  folly::applyTuple(func, argsTuple);
-  folly::applyTuple(func, std::make_tuple(1, 2, 3.0));
-  folly::applyTuple(makeFunc(), std::make_tuple(1, 2, 3.0));
-  folly::applyTuple(makeFunc(), argsTuple);
+  folly::apply(func2, argsTuple);
+  folly::apply(func, argsTuple);
+  folly::apply(func, std::make_tuple(1, 2, 3.0));
+  folly::apply(makeFunc(), std::make_tuple(1, 2, 3.0));
+  folly::apply(makeFunc(), argsTuple);
 
   std::unique_ptr<Wat> wat(new Wat);
-  folly::applyTuple(&Wat::func, std::make_tuple(wat.get(), 1, 2, 3.0));
+  folly::apply(&Wat::func, std::make_tuple(wat.get(), 1, 2, 3.0));
   auto argsTuple2 = std::make_tuple(wat.get(), 1, 2, 3.0);
-  folly::applyTuple(&Wat::func, argsTuple2);
+  folly::apply(&Wat::func, argsTuple2);
 
-  EXPECT_EQ(10.0,
-            folly::applyTuple(&Wat::retVal,
-                              std::make_tuple(wat.get(), 1, 9.0)));
+  EXPECT_EQ(
+      10.0, folly::apply(&Wat::retVal, std::make_tuple(wat.get(), 1, 9.0)));
 
   auto test = guard(func, 1, 2, 3.0);
   CopyCount cpy;
@@ -149,31 +148,32 @@ TEST(ApplyTuple, Test) {
   auto test3 = guard(anotherFunc, std::cref(cpy));
 
   Overloaded ovl;
-  EXPECT_EQ(0,
-            folly::applyTuple(
-              static_cast<int (Overloaded::*)(int)>(&Overloaded::func),
-              std::make_tuple(&ovl, 12)));
+  EXPECT_EQ(
+      0,
+      folly::apply(
+          static_cast<int (Overloaded::*)(int)>(&Overloaded::func),
+          std::make_tuple(&ovl, 12)));
   EXPECT_EQ(
       /* do not code-mode to EXPECT_TRUE */ true,
-      folly::applyTuple(
+      folly::apply(
           static_cast<bool (Overloaded::*)(bool)>(&Overloaded::func),
           std::make_tuple(&ovl, false)));
 
-  int x = folly::applyTuple(std::plus<int>(), std::make_tuple(12, 12));
+  int x = folly::apply(std::plus<int>(), std::make_tuple(12, 12));
   EXPECT_EQ(24, x);
 
   Mover m;
-  folly::applyTuple(move_only_func,
-                    std::forward_as_tuple(std::forward<Mover>(Mover())));
+  folly::apply(
+      move_only_func, std::forward_as_tuple(std::forward<Mover>(Mover())));
   const auto tuple3 = std::make_tuple(1, 2, 3.0);
-  folly::applyTuple(func, tuple3);
+  folly::apply(func, tuple3);
 }
 
 TEST(ApplyTuple, Mutable) {
   auto argsTuple = std::make_tuple(1, 2, 3.0);
 
-  folly::applyTuple([](int a, int b, double c) mutable { func(a, b, c); },
-                    argsTuple);
+  folly::apply(
+      [](int a, int b, double c) mutable { func(a, b, c); }, argsTuple);
 }
 
 TEST(ApplyTuple, ConstOverloads) {
@@ -186,15 +186,15 @@ TEST(ApplyTuple, ConstOverloads) {
   ConstOverloaded covl;
 
   // call operator()()
-  EXPECT_EQ(folly::applyTuple(covl, std::make_tuple()), 101);
-  EXPECT_EQ(folly::applyTuple(std::ref(covl), std::make_tuple()), 101);
-  EXPECT_EQ(folly::applyTuple(std::move(covl), std::make_tuple()), 101);
+  EXPECT_EQ(folly::apply(covl, std::make_tuple()), 101);
+  EXPECT_EQ(folly::apply(std::ref(covl), std::make_tuple()), 101);
+  EXPECT_EQ(folly::apply(std::move(covl), std::make_tuple()), 101);
 
   // call operator()() const
-  EXPECT_EQ(folly::applyTuple(const_cast<ConstOverloaded const&>(covl),
-                              std::make_tuple()),
-            102);
-  EXPECT_EQ(folly::applyTuple(std::cref(covl), std::make_tuple()), 102);
+  EXPECT_EQ(
+      folly::apply(const_cast<ConstOverloaded const&>(covl), std::make_tuple()),
+      102);
+  EXPECT_EQ(folly::apply(std::cref(covl), std::make_tuple()), 102);
 }
 
 TEST(ApplyTuple, RefOverloads) {
@@ -208,17 +208,17 @@ TEST(ApplyTuple, RefOverloads) {
   RefOverloaded rovl;
 
   // call operator()() &
-  EXPECT_EQ(folly::applyTuple(rovl, std::make_tuple()), 201);
-  EXPECT_EQ(folly::applyTuple(std::ref(rovl), std::make_tuple()), 201);
+  EXPECT_EQ(folly::apply(rovl, std::make_tuple()), 201);
+  EXPECT_EQ(folly::apply(std::ref(rovl), std::make_tuple()), 201);
 
   // call operator()() const &
-  EXPECT_EQ(folly::applyTuple(const_cast<RefOverloaded const&>(rovl),
-                              std::make_tuple()),
-            202);
-  EXPECT_EQ(folly::applyTuple(std::cref(rovl), std::make_tuple()), 202);
+  EXPECT_EQ(
+      folly::apply(const_cast<RefOverloaded const&>(rovl), std::make_tuple()),
+      202);
+  EXPECT_EQ(folly::apply(std::cref(rovl), std::make_tuple()), 202);
 
   // call operator()() &&
-  EXPECT_EQ(folly::applyTuple(std::move(rovl), std::make_tuple()), 203);
+  EXPECT_EQ(folly::apply(std::move(rovl), std::make_tuple()), 203);
 }
 
 struct MemberFunc {
@@ -232,20 +232,20 @@ TEST(ApplyTuple, MemberFunction) {
   mf.x = 123;
 
   // call getter
-  EXPECT_EQ(folly::applyTuple(&MemberFunc::getX, std::make_tuple(&mf)), 123);
+  EXPECT_EQ(folly::apply(&MemberFunc::getX, std::make_tuple(&mf)), 123);
 
   // call setter
-  folly::applyTuple(&MemberFunc::setX, std::make_tuple(&mf, 234));
+  folly::apply(&MemberFunc::setX, std::make_tuple(&mf, 234));
   EXPECT_EQ(mf.x, 234);
-  EXPECT_EQ(folly::applyTuple(&MemberFunc::getX, std::make_tuple(&mf)), 234);
+  EXPECT_EQ(folly::apply(&MemberFunc::getX, std::make_tuple(&mf)), 234);
 }
 
 TEST(ApplyTuple, MemberFunctionWithRefWrapper) {
   MemberFunc mf;
   mf.x = 234;
 
-  EXPECT_EQ(folly::applyTuple(&MemberFunc::getX, std::make_tuple(std::ref(mf))),
-            234);
+  EXPECT_EQ(
+      folly::apply(&MemberFunc::getX, std::make_tuple(std::ref(mf))), 234);
 }
 
 TEST(ApplyTuple, MemberFunctionWithConstPointer) {
@@ -253,8 +253,9 @@ TEST(ApplyTuple, MemberFunctionWithConstPointer) {
   mf.x = 234;
 
   EXPECT_EQ(
-      folly::applyTuple(&MemberFunc::getX,
-                        std::make_tuple(const_cast<MemberFunc const*>(&mf))),
+      folly::apply(
+          &MemberFunc::getX,
+          std::make_tuple(const_cast<MemberFunc const*>(&mf))),
       234);
 }
 
@@ -263,8 +264,8 @@ TEST(ApplyTuple, MemberFunctionWithSharedPtr) {
   mf.x = 234;
 
   EXPECT_EQ(
-      folly::applyTuple(&MemberFunc::getX,
-                        std::make_tuple(std::make_shared<MemberFunc>(mf))),
+      folly::apply(
+          &MemberFunc::getX, std::make_tuple(std::make_shared<MemberFunc>(mf))),
       234);
 }
 
@@ -273,47 +274,61 @@ TEST(ApplyTuple, MemberFunctionWithUniquePtr) {
   mf.x = 234;
 
   EXPECT_EQ(
-      folly::applyTuple(&MemberFunc::getX,
-                        std::make_tuple(std::make_unique<MemberFunc>(mf))),
+      folly::apply(
+          &MemberFunc::getX, std::make_tuple(std::make_unique<MemberFunc>(mf))),
       234);
 }
 
 TEST(ApplyTuple, Array) {
-  folly::applyTuple(func, std::array<int, 3>{{1, 2, 3}});
-  folly::applyTuple(func, std::array<double, 3>{{1, 2, 3}});
+  folly::apply(func, std::array<int, 3>{{1, 2, 3}});
+  folly::apply(func, std::array<double, 3>{{1, 2, 3}});
 }
 
 TEST(ApplyTuple, Pair) {
   auto add = [](int x, int y) { return x + y; };
 
-  EXPECT_EQ(folly::applyTuple(add, std::pair<int, int>{1200, 34}), 1234);
+  EXPECT_EQ(folly::apply(add, std::pair<int, int>{1200, 34}), 1234);
 }
 
 TEST(ApplyTuple, MultipleTuples) {
   auto add = [](int x, int y, int z) { return x * 100 + y * 10 + z; };
 
-  EXPECT_EQ(123, folly::applyTuple(add, std::make_tuple(1, 2, 3)));
+  EXPECT_EQ(123, folly::apply(add, std::make_tuple(1, 2, 3)));
   EXPECT_EQ(
-      123, folly::applyTuple(add, std::make_tuple(1, 2, 3), std::make_tuple()));
+      123,
+      folly::apply(
+          add, std::tuple_cat(std::make_tuple(1, 2, 3), std::make_tuple())));
   EXPECT_EQ(
-      123, folly::applyTuple(add, std::make_tuple(1, 2), std::make_tuple(3)));
+      123,
+      folly::apply(
+          add, std::tuple_cat(std::make_tuple(1, 2), std::make_tuple(3))));
   EXPECT_EQ(
-      123, folly::applyTuple(add, std::make_tuple(1), std::make_tuple(2, 3)));
+      123,
+      folly::apply(
+          add, std::tuple_cat(std::make_tuple(1), std::make_tuple(2, 3))));
   EXPECT_EQ(
-      123, folly::applyTuple(add, std::make_tuple(), std::make_tuple(1, 2, 3)));
+      123,
+      folly::apply(
+          add, std::tuple_cat(std::make_tuple(), std::make_tuple(1, 2, 3))));
 
   EXPECT_EQ(
       123,
-      folly::applyTuple(
-          add, std::make_tuple(1, 2, 3), std::make_tuple(), std::make_tuple()));
+      folly::apply(
+          add,
+          std::tuple_cat(
+              std::make_tuple(1, 2, 3), std::make_tuple(), std::make_tuple())));
   EXPECT_EQ(
       123,
-      folly::applyTuple(
-          add, std::make_tuple(1), std::make_tuple(2), std::make_tuple(3)));
+      folly::apply(
+          add,
+          std::tuple_cat(
+              std::make_tuple(1), std::make_tuple(2), std::make_tuple(3))));
   EXPECT_EQ(
       123,
-      folly::applyTuple(
-          add, std::make_tuple(1), std::make_tuple(), std::make_tuple(2, 3)));
+      folly::apply(
+          add,
+          std::tuple_cat(
+              std::make_tuple(1), std::make_tuple(), std::make_tuple(2, 3))));
 }
 
 TEST(ApplyTuple, UncurryCopyMove) {

folly/hash/Hash.h

@@ -566,7 +566,7 @@ struct IsAvalanchingHasher<hasher<std::pair<T1, T2>>, K> : std::true_type {};
 template <typename... Ts>
 struct hasher<std::tuple<Ts...>> {
   size_t operator()(const std::tuple<Ts...>& key) const {
-    return applyTuple(Hash(), key);
+    return apply(Hash(), key);
   }
 };