C++11 support for Replaceable

Summary: Also add tests for the `is_replaceable` trait.

Reviewed By: yfeldblum

Differential Revision: D5526317

fbshipit-source-id: 92559d55fbb8d115856ef9e8f86b42e327f74e56

folly/FixedString.h

@@ -28,29 +28,12 @@
 #include <type_traits>
 #include <utility>
 
+#include <folly/Portability.h>
 #include <folly/Range.h>
 #include <folly/Utility.h>
 #include <folly/portability/BitsFunctexcept.h>
 #include <folly/portability/Constexpr.h>
 
-// Define FOLLY_USE_CPP14_CONSTEXPR to be true if the compiler's C++14
-// constexpr support is "good enough".
-#ifndef FOLLY_USE_CPP14_CONSTEXPR
-#if defined(__clang__)
-#define FOLLY_USE_CPP14_CONSTEXPR __cplusplus >= 201300L
-#elif defined(__GNUC__)
-#define FOLLY_USE_CPP14_CONSTEXPR __cplusplus >= 201304L
-#else
-#define FOLLY_USE_CPP14_CONSTEXPR 0 // MSVC?
-#endif
-#endif
-
-#if FOLLY_USE_CPP14_CONSTEXPR
-#define FOLLY_CPP14_CONSTEXPR constexpr
-#else
-#define FOLLY_CPP14_CONSTEXPR inline
-#endif
-
 namespace folly {
 
 template <class Char, std::size_t N>

folly/Portability.h

@@ -407,3 +407,21 @@ constexpr auto kIsWindows = false;
 constexpr auto kMscVer = 0;
 #endif
 }
+
+// Define FOLLY_USE_CPP14_CONSTEXPR to be true if the compiler's C++14
+// constexpr support is "good enough".
+#ifndef FOLLY_USE_CPP14_CONSTEXPR
+#if defined(__clang__)
+#define FOLLY_USE_CPP14_CONSTEXPR __cplusplus >= 201300L
+#elif defined(__GNUC__)
+#define FOLLY_USE_CPP14_CONSTEXPR __cplusplus >= 201304L
+#else
+#define FOLLY_USE_CPP14_CONSTEXPR 0 // MSVC?
+#endif
+#endif
+
+#if FOLLY_USE_CPP14_CONSTEXPR
+#define FOLLY_CPP14_CONSTEXPR constexpr
+#else
+#define FOLLY_CPP14_CONSTEXPR inline
+#endif

folly/Replaceable.h

@@ -22,6 +22,7 @@
 #include <utility>
 
 #include <folly/Launder.h>
+#include <folly/Portability.h>
 #include <folly/Traits.h>
 #include <folly/Utility.h>
 
@@ -450,7 +451,7 @@ class alignas(T) Replaceable
   template <
       class... Args,
       std::enable_if_t<std::is_constructible<T, Args&&...>::value, int> = 0>
-  constexpr explicit Replaceable(in_place_t, Args&&... args)
+  FOLLY_CPP14_CONSTEXPR explicit Replaceable(in_place_t, Args&&... args)
       // clang-format off
       noexcept(std::is_nothrow_constructible<T, Args&&...>::value)
       // clang-format on
@@ -464,7 +465,7 @@ class alignas(T) Replaceable
       std::enable_if_t<
           std::is_constructible<T, std::initializer_list<U>, Args&&...>::value,
           int> = 0>
-  constexpr explicit Replaceable(
+  FOLLY_CPP14_CONSTEXPR explicit Replaceable(
       in_place_t,
       std::initializer_list<U> il,
       Args&&... args)
@@ -486,7 +487,7 @@ class alignas(T) Replaceable
               !std::is_same<Replaceable<T>, std::decay_t<U>>::value &&
               std::is_convertible<U&&, T>::value,
           int> = 0>
-  constexpr /* implicit */ Replaceable(U&& other)
+  FOLLY_CPP14_CONSTEXPR /* implicit */ Replaceable(U&& other)
       // clang-format off
       noexcept(std::is_nothrow_constructible<T, U&&>::value)
       // clang-format on
@@ -502,7 +503,7 @@ class alignas(T) Replaceable
               !std::is_same<Replaceable<T>, std::decay_t<U>>::value &&
               !std::is_convertible<U&&, T>::value,
           int> = 0>
-  explicit constexpr Replaceable(U&& other)
+  FOLLY_CPP14_CONSTEXPR explicit Replaceable(U&& other)
       // clang-format off
       noexcept(std::is_nothrow_constructible<T, U&&>::value)
       // clang-format on
@@ -622,7 +623,7 @@ class alignas(T) Replaceable
     return launder(reinterpret_cast<T const*>(storage_));
   }
 
-  constexpr T* operator->() {
+  FOLLY_CPP14_CONSTEXPR T* operator->() {
     return launder(reinterpret_cast<T*>(storage_));
   }
 
@@ -630,11 +631,11 @@ class alignas(T) Replaceable
     return *launder(reinterpret_cast<T const*>(storage_));
   }
 
-  constexpr T& operator*() & {
+  FOLLY_CPP14_CONSTEXPR T& operator*() & {
     return *launder(reinterpret_cast<T*>(storage_));
   }
 
-  constexpr T&& operator*() && {
+  FOLLY_CPP14_CONSTEXPR T&& operator*() && {
     return std::move(*launder(reinterpret_cast<T*>(storage_)));
   }
 

folly/test/ReplaceableTest.cpp

@@ -170,6 +170,10 @@ TYPED_TEST(ReplaceableStaticAttributeTest, nothrow_copy_assignable) {
           std::is_nothrow_copy_constructible<TypeParam>::value,
       std::is_nothrow_copy_assignable<Replaceable<TypeParam>>::value);
 }
+TYPED_TEST(ReplaceableStaticAttributeTest, replaceable) {
+  EXPECT_FALSE(is_replaceable<TypeParam>::value);
+  EXPECT_TRUE(is_replaceable<Replaceable<TypeParam>>::value);
+}
 
 TYPED_TEST(ReplaceableStaticAttributePairTest, copy_construct) {
   using T = typename TypeParam::first_type;