folly::Function: fix swap function and put in correct namespace

Summary:The swap function belongs in the same namespace as Function: folly.
Also, to avoid amibiguities with a generic swap function in
<algorithm>, we need two variants: one for identical types of
folly::Function, and one for folly::Functions with different
configurations.

Reviewed By: ericniebler

Differential Revision: D3106429

fb-gh-sync-id: 11b04e9bc709d52016ac94c078278410f5ee43c6
fbshipit-source-id: 11b04e9bc709d52016ac94c078278410f5ee43c6

folly/Function.h

@@ -532,15 +532,25 @@ constCastFunction(Function<FunctionType, NTM, EmbedFunctorSize>&&
   return std::move(from).castToConstFunction();
 }
 
-} // folly
+template <typename FunctionType, FunctionMoveCtor NOM, size_t S>
+void swap(
+    Function<FunctionType, NOM, S>& lhs,
+    Function<FunctionType, NOM, S>& rhs) noexcept(noexcept(lhs.swap(rhs))) {
+  lhs.swap(rhs);
+}
 
-namespace std {
-template <typename FunctionType, bool NOM1, bool NOM2, size_t S1, size_t S2>
+template <
+    typename FunctionType,
+    FunctionMoveCtor NOM1,
+    FunctionMoveCtor NOM2,
+    size_t S1,
+    size_t S2>
 void swap(
-    ::folly::Function<FunctionType, NOM1, S1>& lhs,
-    ::folly::Function<FunctionType, NOM2, S2>& rhs) {
+    Function<FunctionType, NOM1, S1>& lhs,
+    Function<FunctionType, NOM2, S2>& rhs) noexcept(noexcept(lhs.swap(rhs))) {
   lhs.swap(rhs);
 }
-} // std
+
+} // namespace folly
 
 #include "Function-inl.h"

folly/test/FunctionTest.cpp

@@ -266,7 +266,7 @@ TEST(Function, Types) {
 // TEST =====================================================================
 // Swap
 
-template <FunctionMoveCtor NEM1, FunctionMoveCtor NEM2>
+template <FunctionMoveCtor NEM1, FunctionMoveCtor NEM2, bool UseSwapMethod>
 void swap_test() {
   Function<int(int), NEM1> mf1(func_int_int_add_25);
   Function<int(int), NEM2> mf2(func_int_int_add_111);
@@ -274,7 +274,11 @@ void swap_test() {
   EXPECT_EQ(mf1(100), 125);
   EXPECT_EQ(mf2(100), 211);
 
+  if (UseSwapMethod) {
     mf1.swap(mf2);
+  } else {
+    swap(mf1, mf2);
+  }
 
   EXPECT_EQ(mf2(100), 125);
   EXPECT_EQ(mf1(100), 211);
@@ -282,7 +286,11 @@ void swap_test() {
   Function<int(int)> mf3(nullptr);
   EXPECT_EQ(mf3, nullptr);
 
+  if (UseSwapMethod) {
     mf1.swap(mf3);
+  } else {
+    swap(mf1, mf3);
+  }
 
   EXPECT_EQ(mf3(100), 211);
   EXPECT_EQ(mf1, nullptr);
@@ -290,25 +298,45 @@ void swap_test() {
   Function<int(int)> mf4([](int x) { return x + 222; });
   EXPECT_EQ(mf4(100), 322);
 
+  if (UseSwapMethod) {
     mf4.swap(mf3);
+  } else {
+    swap(mf4, mf3);
+  }
   EXPECT_EQ(mf4(100), 211);
   EXPECT_EQ(mf3(100), 322);
 
+  if (UseSwapMethod) {
     mf3.swap(mf1);
+  } else {
+    swap(mf3, mf1);
+  }
   EXPECT_EQ(mf3, nullptr);
   EXPECT_EQ(mf1(100), 322);
 }
-TEST(Function, Swap_TT) {
-  swap_test<FunctionMoveCtor::MAY_THROW, FunctionMoveCtor::MAY_THROW>();
+TEST(Function, SwapMethod_TT) {
+  swap_test<FunctionMoveCtor::MAY_THROW, FunctionMoveCtor::MAY_THROW, true>();
+}
+TEST(Function, SwapMethod_TN) {
+  swap_test<FunctionMoveCtor::MAY_THROW, FunctionMoveCtor::NO_THROW, true>();
+}
+TEST(Function, SwapMethod_NT) {
+  swap_test<FunctionMoveCtor::NO_THROW, FunctionMoveCtor::MAY_THROW, true>();
+}
+TEST(Function, SwapMethod_NN) {
+  swap_test<FunctionMoveCtor::NO_THROW, FunctionMoveCtor::NO_THROW, true>();
+}
+TEST(Function, SwapFunction_TT) {
+  swap_test<FunctionMoveCtor::MAY_THROW, FunctionMoveCtor::MAY_THROW, false>();
 }
-TEST(Function, Swap_TN) {
-  swap_test<FunctionMoveCtor::MAY_THROW, FunctionMoveCtor::NO_THROW>();
+TEST(Function, SwapFunction_TN) {
+  swap_test<FunctionMoveCtor::MAY_THROW, FunctionMoveCtor::NO_THROW, false>();
 }
-TEST(Function, Swap_NT) {
-  swap_test<FunctionMoveCtor::NO_THROW, FunctionMoveCtor::MAY_THROW>();
+TEST(Function, SwapFunction_NT) {
+  swap_test<FunctionMoveCtor::NO_THROW, FunctionMoveCtor::MAY_THROW, false>();
 }
-TEST(Function, Swap_NN) {
-  swap_test<FunctionMoveCtor::NO_THROW, FunctionMoveCtor::NO_THROW>();
+TEST(Function, SwapFunction_NN) {
+  swap_test<FunctionMoveCtor::NO_THROW, FunctionMoveCtor::NO_THROW, false>();
 }
 
 // TEST =====================================================================