X-Git-Url: http://plrg.eecs.uci.edu/git/?p=folly.git;a=blobdiff_plain;f=folly%2FTraits.h;h=fb797f377bb72a7f860180c8ea511066c15ce0c5;hp=bc0a0bf68847f1270b389eb9a87d5a6b3ce2088e;hb=6ae2206d4a23d683877e33919a469abfdfc411e5;hpb=1bf1654c689b31ac7b53f499b8f1810548fbda7a

diff --git a/folly/Traits.h b/folly/Traits.h
index bc0a0bf6..fb797f37 100644
--- a/folly/Traits.h
+++ b/folly/Traits.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,21 +16,221 @@
 
 // @author: Andrei Alexandrescu
 
-#ifndef FOLLY_BASE_TRAITS_H_
-#define FOLLY_BASE_TRAITS_H_
+#pragma once
 
+#include <functional>
+#include <limits>
 #include <memory>
 #include <type_traits>
 
+#include <folly/Portability.h>
+
+// libc++ doesn't provide this header, nor does msvc
+#ifdef FOLLY_HAVE_BITS_CXXCONFIG_H
+// This file appears in two locations: inside fbcode and in the
+// libstdc++ source code (when embedding fbstring as std::string).
+// To aid in this schizophrenic use, two macros are defined in
+// c++config.h:
+//   _LIBSTDCXX_FBSTRING - Set inside libstdc++.  This is useful to
+//      gate use inside fbcode v. libstdc++
 #include <bits/c++config.h>
+#endif
 
-#include <boost/type_traits.hpp>
-#include <boost/mpl/and.hpp>
-#include <boost/mpl/has_xxx.hpp>
-#include <boost/mpl/not.hpp>
+#define FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(classname, type_name)              \
+  template <typename TTheClass_>                                               \
+  struct classname##__folly_traits_impl__ {                                    \
+    template <typename UTheClass_>                                             \
+    static constexpr bool test(typename UTheClass_::type_name*) {              \
+      return true;                                                             \
+    }                                                                          \
+    template <typename>                                                        \
+    static constexpr bool test(...) {                                          \
+      return false;                                                            \
+    }                                                                          \
+  };                                                                           \
+  template <typename TTheClass_>                                               \
+  using classname = typename std::conditional<                                 \
+      classname##__folly_traits_impl__<TTheClass_>::template test<TTheClass_>( \
+          nullptr),                                                            \
+      std::true_type,                                                          \
+      std::false_type>::type;
+
+#define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, cv_qual) \
+  template <typename TTheClass_, typename RTheReturn_, typename... TTheArgs_> \
+  struct classname##__folly_traits_impl__<                                    \
+      TTheClass_,                                                             \
+      RTheReturn_(TTheArgs_...) cv_qual> {                                    \
+    template <                                                                \
+        typename UTheClass_,                                                  \
+        RTheReturn_ (UTheClass_::*)(TTheArgs_...) cv_qual>                    \
+    struct sfinae {};                                                         \
+    template <typename UTheClass_>                                            \
+    static std::true_type test(sfinae<UTheClass_, &UTheClass_::func_name>*);  \
+    template <typename>                                                       \
+    static std::false_type test(...);                                         \
+  }
+
+/*
+ * The FOLLY_CREATE_HAS_MEMBER_FN_TRAITS is used to create traits
+ * classes that check for the existence of a member function with
+ * a given name and signature. It currently does not support
+ * checking for inherited members.
+ *
+ * Such classes receive two template parameters: the class to be checked
+ * and the signature of the member function. A static boolean field
+ * named `value` (which is also constexpr) tells whether such member
+ * function exists.
+ *
+ * Each traits class created is bound only to the member name, not to
+ * its signature nor to the type of the class containing it.
+ *
+ * Say you need to know if a given class has a member function named
+ * `test` with the following signature:
+ *
+ *    int test() const;
+ *
+ * You'd need this macro to create a traits class to check for a member
+ * named `test`, and then use this traits class to check for the signature:
+ *
+ * namespace {
+ *
+ * FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(has_test_traits, test);
+ *
+ * } // unnamed-namespace
+ *
+ * void some_func() {
+ *   cout << "Does class Foo have a member int test() const? "
+ *     << boolalpha << has_test_traits<Foo, int() const>::value;
+ * }
+ *
+ * You can use the same traits class to test for a completely different
+ * signature, on a completely different class, as long as the member name
+ * is the same:
+ *
+ * void some_func() {
+ *   cout << "Does class Foo have a member int test()? "
+ *     << boolalpha << has_test_traits<Foo, int()>::value;
+ *   cout << "Does class Foo have a member int test() const? "
+ *     << boolalpha << has_test_traits<Foo, int() const>::value;
+ *   cout << "Does class Bar have a member double test(const string&, long)? "
+ *     << boolalpha << has_test_traits<Bar, double(const string&, long)>::value;
+ * }
+ *
+ * @author: Marcelo Juchem <marcelo@fb.com>
+ */
+#define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(classname, func_name)               \
+  template <typename, typename>                                               \
+  struct classname##__folly_traits_impl__;                                    \
+  FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, );             \
+  FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, const);        \
+  FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(                                     \
+      classname, func_name, /* nolint */ volatile);                           \
+  FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(                                     \
+      classname, func_name, /* nolint */ volatile const);                     \
+  template <typename TTheClass_, typename TTheSignature_>                     \
+  using classname =                                                           \
+      decltype(classname##__folly_traits_impl__<TTheClass_, TTheSignature_>:: \
+                   template test<TTheClass_>(nullptr))
 
 namespace folly {
 
+/***
+ *  _t
+ *
+ *  Instead of:
+ *
+ *    using decayed = typename std::decay<T>::type;
+ *
+ *  With the C++14 standard trait aliases, we could use:
+ *
+ *    using decayed = std::decay_t<T>;
+ *
+ *  Without them, we could use:
+ *
+ *    using decayed = _t<std::decay<T>>;
+ *
+ *  Also useful for any other library with template types having dependent
+ *  member types named `type`, like the standard trait types.
+ */
+template <typename T>
+using _t = typename T::type;
+
+/**
+ *  type_t
+ *
+ *  A type alias for the first template type argument. `type_t` is useful for
+ *  controlling class-template and function-template partial specialization.
+ *
+ *  Example:
+ *
+ *    template <typename Value>
+ *    class Container {
+ *     public:
+ *      template <typename... Args>
+ *      Container(
+ *          type_t<in_place_t, decltype(Value(std::declval<Args>()...))>,
+ *          Args&&...);
+ *    };
+ *
+ *  void_t
+ *
+ *  A type alias for `void`. `void_t` is useful for controling class-template
+ *  and function-template partial specialization.
+ *
+ *  Example:
+ *
+ *    // has_value_type<T>::value is true if T has a nested type `value_type`
+ *    template <class T, class = void>
+ *    struct has_value_type
+ *        : std::false_type {};
+ *
+ *    template <class T>
+ *    struct has_value_type<T, folly::void_t<typename T::value_type>>
+ *        : std::true_type {};
+ */
+
+/**
+ * There is a bug in libstdc++, libc++, and MSVC's STL that causes it to
+ * ignore unused template parameter arguments in template aliases and does not
+ * cause substitution failures. This defect has been recorded here:
+ * http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1558.
+ *
+ * This causes the implementation of std::void_t to be buggy, as it is likely
+ * defined as something like the following:
+ *
+ *  template <typename...>
+ *  using void_t = void;
+ *
+ * This causes the compiler to ignore all the template arguments and does not
+ * help when one wants to cause substitution failures.  Rather declarations
+ * which have void_t in orthogonal specializations are treated as the same.
+ * For example, assuming the possible `T` types are only allowed to have
+ * either the alias `one` or `two` and never both or none:
+ *
+ *  template <typename T,
+ *            typename std::void_t<std::decay_t<T>::one>* = nullptr>
+ *  void foo(T&&) {}
+ *  template <typename T,
+ *            typename std::void_t<std::decay_t<T>::two>* = nullptr>
+ *  void foo(T&&) {}
+ *
+ * The second foo() will be a redefinition because it conflicts with the first
+ * one; void_t does not cause substitution failures - the template types are
+ * just ignored.
+ */
+
+namespace traits_detail {
+template <class T, class...>
+struct type_t_ {
+  using type = T;
+};
+} // namespace traits_detail
+
+template <class T, class... Ts>
+using type_t = typename traits_detail::type_t_<T, Ts...>::type;
+template <class... Ts>
+using void_t = type_t<void, Ts...>;
+
 /**
  * IsRelocatable<T>::value describes the ability of moving around
  * memory a value of type T by using memcpy (as opposed to the
@@ -80,44 +280,161 @@ namespace folly {
 
 namespace traits_detail {
 
-#define FOLLY_HAS_TRUE_XXX(name)                          \
-  BOOST_MPL_HAS_XXX_TRAIT_DEF(name);                      \
-  template <class T> struct name ## _is_true              \
-    : std::is_same<typename T::name, std::true_type> {};  \
-  template <class T> struct has_true_ ## name             \
-    : std::conditional<                                   \
-        has_ ## name <T>::value,                          \
-        name ## _is_true<T>,                              \
-        std::false_type                                   \
-      >:: type {};
+#define FOLLY_HAS_TRUE_XXX(name)                                             \
+  FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(has_##name, name);                     \
+  template <class T>                                                         \
+  struct name##_is_true : std::is_same<typename T::name, std::true_type> {}; \
+  template <class T>                                                         \
+  struct has_true_##name : std::conditional<                                 \
+                               has_##name<T>::value,                         \
+                               name##_is_true<T>,                            \
+                               std::false_type>::type {};
 
 FOLLY_HAS_TRUE_XXX(IsRelocatable)
 FOLLY_HAS_TRUE_XXX(IsZeroInitializable)
 FOLLY_HAS_TRUE_XXX(IsTriviallyCopyable)
 
 #undef FOLLY_HAS_TRUE_XXX
-}
+
+// Older versions of libstdc++ do not provide std::is_trivially_copyable
+#if defined(__clang__) && !defined(_LIBCPP_VERSION)
+template <class T>
+struct is_trivially_copyable
+    : std::integral_constant<bool, __is_trivially_copyable(T)> {};
+#elif defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 5
+template <class T>
+struct is_trivially_copyable : std::is_trivial<T> {};
+#else
+template <class T>
+using is_trivially_copyable = std::is_trivially_copyable<T>;
+#endif
+} // namespace traits_detail
+
+struct Ignore {
+  Ignore() = default;
+  template <class T>
+  constexpr /* implicit */ Ignore(const T&) {}
+  template <class T>
+  const Ignore& operator=(T const&) const { return *this; }
+};
+
+template <class...>
+using Ignored = Ignore;
+
+namespace traits_detail_IsEqualityComparable {
+Ignore operator==(Ignore, Ignore);
+
+template <class T, class U = T>
+struct IsEqualityComparable
+    : std::is_convertible<
+          decltype(std::declval<T>() == std::declval<U>()),
+          bool
+      > {};
+} // namespace traits_detail_IsEqualityComparable
+
+/* using override */ using traits_detail_IsEqualityComparable::
+    IsEqualityComparable;
+
+namespace traits_detail_IsLessThanComparable {
+Ignore operator<(Ignore, Ignore);
+
+template <class T, class U = T>
+struct IsLessThanComparable
+    : std::is_convertible<
+          decltype(std::declval<T>() < std::declval<U>()),
+          bool
+      > {};
+} // namespace traits_detail_IsLessThanComparable
+
+/* using override */ using traits_detail_IsLessThanComparable::
+    IsLessThanComparable;
+
+namespace traits_detail_IsNothrowSwappable {
+#if defined(__cpp_lib_is_swappable) || (_CPPLIB_VER && _HAS_CXX17)
+// MSVC 2015+ already implements the C++17 P0185R1 proposal which
+// adds std::is_nothrow_swappable, so use it instead if C++17 mode
+// is enabled.
+template <typename T>
+using IsNothrowSwappable = std::is_nothrow_swappable<T>;
+#elif _CPPLIB_VER
+// MSVC 2015+ defines the base even if C++17 is disabled, and
+// MSVC 2015 has issues with our fallback implementation due to
+// over-eager evaluation of noexcept.
+template <typename T>
+using IsNothrowSwappable = std::_Is_nothrow_swappable<T>;
+#else
+/* using override */ using std::swap;
+
+template <class T>
+struct IsNothrowSwappable
+    : std::integral_constant<bool,
+        std::is_nothrow_move_constructible<T>::value &&
+        noexcept(swap(std::declval<T&>(), std::declval<T&>()))
+      > {};
+#endif
+} // namespace traits_detail_IsNothrowSwappable
+
+/* using override */ using traits_detail_IsNothrowSwappable::IsNothrowSwappable;
 
 template <class T> struct IsTriviallyCopyable
-  : std::integral_constant<bool,
-      !std::is_class<T>::value ||
-      // TODO: add alternate clause is_trivially_copyable, when available
-      traits_detail::has_true_IsTriviallyCopyable<T>::value
-    > {};
+  : std::conditional<
+      traits_detail::has_IsTriviallyCopyable<T>::value,
+      traits_detail::has_true_IsTriviallyCopyable<T>,
+      traits_detail::is_trivially_copyable<T>
+    >::type {};
 
 template <class T> struct IsRelocatable
-  : std::integral_constant<bool,
-      !std::is_class<T>::value ||
+  : std::conditional<
+      traits_detail::has_IsRelocatable<T>::value,
+      traits_detail::has_true_IsRelocatable<T>,
       // TODO add this line (and some tests for it) when we upgrade to gcc 4.7
       //std::is_trivially_move_constructible<T>::value ||
-      IsTriviallyCopyable<T>::value ||
-      traits_detail::has_true_IsRelocatable<T>::value
-    > {};
+      IsTriviallyCopyable<T>
+    >::type {};
 
 template <class T> struct IsZeroInitializable
-  : std::integral_constant<bool,
-      !std::is_class<T>::value ||
-      traits_detail::has_true_IsZeroInitializable<T>::value
+  : std::conditional<
+      traits_detail::has_IsZeroInitializable<T>::value,
+      traits_detail::has_true_IsZeroInitializable<T>,
+      std::integral_constant<bool, !std::is_class<T>::value>
+    >::type {};
+
+template <typename...>
+struct Conjunction : std::true_type {};
+template <typename T>
+struct Conjunction<T> : T {};
+template <typename T, typename... TList>
+struct Conjunction<T, TList...>
+    : std::conditional<T::value, Conjunction<TList...>, T>::type {};
+
+template <typename...>
+struct Disjunction : std::false_type {};
+template <typename T>
+struct Disjunction<T> : T {};
+template <typename T, typename... TList>
+struct Disjunction<T, TList...>
+    : std::conditional<T::value, T, Disjunction<TList...>>::type {};
+
+template <typename T>
+struct Negation : std::integral_constant<bool, !T::value> {};
+
+template <bool... Bs>
+struct Bools {
+  using valid_type = bool;
+  static constexpr std::size_t size() {
+    return sizeof...(Bs);
+  }
+};
+
+// Lighter-weight than Conjunction, but evaluates all sub-conditions eagerly.
+template <class... Ts>
+struct StrictConjunction
+    : std::is_same<Bools<Ts::value...>, Bools<(Ts::value || true)...>> {};
+
+template <class... Ts>
+struct StrictDisjunction
+  : Negation<
+      std::is_same<Bools<Ts::value...>, Bools<(Ts::value && false)...>>
     > {};
 
 } // namespace folly
@@ -127,41 +444,24 @@ template <class T> struct IsZeroInitializable
  * regular type, use it like this:
  *
  * // Make sure you're at namespace ::folly scope
- * template<> FOLLY_ASSUME_RELOCATABLE(MyType)
+ * template <> FOLLY_ASSUME_RELOCATABLE(MyType)
  *
  * When using it with a template type, use it like this:
  *
  * // Make sure you're at namespace ::folly scope
- * template<class T1, class T2>
+ * template <class T1, class T2>
  * FOLLY_ASSUME_RELOCATABLE(MyType<T1, T2>)
  */
 #define FOLLY_ASSUME_RELOCATABLE(...) \
   struct IsRelocatable<  __VA_ARGS__ > : std::true_type {};
 
 /**
- * Use this macro ONLY inside namespace boost. When using it with a
- * regular type, use it like this:
- *
- * // Make sure you're at namespace ::boost scope
- * template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType)
- *
- * When using it with a template type, use it like this:
- *
- * // Make sure you're at namespace ::boost scope
- * template<class T1, class T2>
- * FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType<T1, T2>)
- */
-#define FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(...) \
-  struct has_nothrow_constructor<  __VA_ARGS__ > : ::boost::true_type {};
-
-/**
- * The FOLLY_ASSUME_FBVECTOR_COMPATIBLE* macros below encode two
- * assumptions: first, that the type is relocatable per IsRelocatable
- * above, and that it has a nothrow constructor. Most types can be
- * assumed to satisfy both conditions, but it is the responsibility of
- * the user to state that assumption. User-defined classes will not
- * work with fbvector (see FBVector.h) unless they state this
- * combination of properties.
+ * The FOLLY_ASSUME_FBVECTOR_COMPATIBLE* macros below encode the
+ * assumption that the type is relocatable per IsRelocatable
+ * above. Many types can be assumed to satisfy this condition, but
+ * it is the responsibility of the user to state that assumption.
+ * User-defined classes will not be optimized for use with
+ * fbvector (see FBVector.h) unless they state that assumption.
  *
  * Use FOLLY_ASSUME_FBVECTOR_COMPATIBLE with regular types like this:
  *
@@ -180,40 +480,35 @@ template <class T> struct IsZeroInitializable
  */
 
 // Use this macro ONLY at global level (no namespace)
-#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE(...)                           \
-  namespace folly { template<> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__) }   \
-  namespace boost { \
-  template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__) }
+#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE(...) \
+  namespace folly {                           \
+  template <>                                 \
+  FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__)       \
+  }
 // Use this macro ONLY at global level (no namespace)
-#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(...)                         \
-  namespace folly {                                                     \
-  template <class T1> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1>) }       \
-    namespace boost {                                                   \
-    template <class T1> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1>) }
+#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(...) \
+  namespace folly {                             \
+  template <class T1>                           \
+  FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1>)     \
+  }
 // Use this macro ONLY at global level (no namespace)
-#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(...)                 \
-  namespace folly {                                             \
-  template <class T1, class T2>                                 \
-  FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2>) }               \
-    namespace boost {                                           \
-    template <class T1, class T2>                               \
-    FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2>) }
+#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(...) \
+  namespace folly {                             \
+  template <class T1, class T2>                 \
+  FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2>) \
+  }
 // Use this macro ONLY at global level (no namespace)
-#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(...)                         \
-  namespace folly {                                                     \
-  template <class T1, class T2, class T3>                               \
-  FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3>) }                   \
-    namespace boost {                                                   \
-    template <class T1, class T2, class T3>                             \
-    FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3>) }
+#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(...)     \
+  namespace folly {                                 \
+  template <class T1, class T2, class T3>           \
+  FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3>) \
+  }
 // Use this macro ONLY at global level (no namespace)
-#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_4(...)                         \
-  namespace folly {                                                     \
-  template <class T1, class T2, class T3, class T4>                     \
-  FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3, T4>) }               \
-    namespace boost {                                                   \
-    template <class T1, class T2, class T3, class T4>                   \
-    FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3, T4>) }
+#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_4(...)         \
+  namespace folly {                                     \
+  template <class T1, class T2, class T3, class T4>     \
+  FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3, T4>) \
+  }
 
 /**
  * Instantiate FOLLY_ASSUME_FBVECTOR_COMPATIBLE for a few types. It is
@@ -222,13 +517,15 @@ template <class T> struct IsZeroInitializable
  * although that is not guaranteed by the standard.
  */
 
-namespace std {
+FOLLY_NAMESPACE_STD_BEGIN
 
 template <class T, class U>
   struct pair;
 #ifndef _GLIBCXX_USE_FB
+FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
 template <class T, class R, class A>
   class basic_string;
+FOLLY_GLIBCXX_NAMESPACE_CXX11_END
 #else
 template <class T, class R, class A, class S>
   class basic_string;
@@ -237,8 +534,10 @@ template <class T, class A>
   class vector;
 template <class T, class A>
   class deque;
+FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
 template <class T, class A>
   class list;
+FOLLY_GLIBCXX_NAMESPACE_CXX11_END
 template <class T, class C, class A>
   class set;
 template <class K, class V, class C, class A>
@@ -246,41 +545,29 @@ template <class K, class V, class C, class A>
 template <class T>
   class shared_ptr;
 
-}
-
-namespace boost {
-
-template <class T> class shared_ptr;
-
-template <class T, class U>
-struct has_nothrow_constructor< std::pair<T, U> >
-    : ::boost::mpl::and_< has_nothrow_constructor<T>,
-                          has_nothrow_constructor<U> > {};
-
-} // namespace boost
+FOLLY_NAMESPACE_STD_END
 
 namespace folly {
 
 // STL commonly-used types
 template <class T, class U>
-struct IsRelocatable<  std::pair<T, U> >
-    : ::boost::mpl::and_< IsRelocatable<T>, IsRelocatable<U> > {};
+struct IsRelocatable< std::pair<T, U> >
+    : std::integral_constant<bool,
+        IsRelocatable<T>::value &&
+        IsRelocatable<U>::value> {};
 
 // Is T one of T1, T2, ..., Tn?
-template <class T, class... Ts>
-struct IsOneOf {
-  enum { value = false };
-};
-
-template <class T, class T1, class... Ts>
-struct IsOneOf<T, T1, Ts...> {
-  enum { value = std::is_same<T, T1>::value || IsOneOf<T, Ts...>::value };
-};
+template <typename T, typename... Ts>
+using IsOneOf = StrictDisjunction<std::is_same<T, Ts>...>;
 
 /*
- * Complementary type traits to check for a negative/non-positive value.
+ * Complementary type traits for integral comparisons.
  *
- * `if(x < 0)` yields an error in clang for unsigned types when -Werror is used
+ * For instance, `if(x < 0)` yields an error in clang for unsigned types
+ *  when -Werror is used due to -Wtautological-compare
+ *
+ *
+ * @author: Marcelo Juchem <marcelo@fb.com>
  */
 
 namespace detail {
@@ -292,10 +579,40 @@ struct is_negative_impl {
 
 template <typename T>
 struct is_negative_impl<T, false> {
-  constexpr static bool check(T x) { return false; }
+  constexpr static bool check(T) { return false; }
 };
 
-} // namespace detail {
+// folly::to integral specializations can end up generating code
+// inside what are really static ifs (not executed because of the templated
+// types) that violate -Wsign-compare and/or -Wbool-compare so suppress them
+// in order to not prevent all calling code from using it.
+FOLLY_PUSH_WARNING
+FOLLY_GCC_DISABLE_WARNING("-Wsign-compare")
+#if __GNUC_PREREQ(5, 0)
+FOLLY_GCC_DISABLE_WARNING("-Wbool-compare")
+#endif
+FOLLY_MSVC_DISABLE_WARNING(4388) // sign-compare
+FOLLY_MSVC_DISABLE_WARNING(4804) // bool-compare
+
+template <typename RHS, RHS rhs, typename LHS>
+bool less_than_impl(LHS const lhs) {
+  return
+    rhs > std::numeric_limits<LHS>::max() ? true :
+    rhs <= std::numeric_limits<LHS>::min() ? false :
+    lhs < rhs;
+}
+
+template <typename RHS, RHS rhs, typename LHS>
+bool greater_than_impl(LHS const lhs) {
+  return
+    rhs > std::numeric_limits<LHS>::max() ? false :
+    rhs < std::numeric_limits<LHS>::min() ? true :
+    lhs > rhs;
+}
+
+FOLLY_POP_WARNING
+
+} // namespace detail
 
 // same as `x < 0`
 template <typename T>
@@ -307,87 +624,83 @@ constexpr bool is_negative(T x) {
 template <typename T>
 constexpr bool is_non_positive(T x) { return !x || folly::is_negative(x); }
 
-} // namespace folly
+// same as `x > 0`
+template <typename T>
+constexpr bool is_positive(T x) { return !is_non_positive(x); }
 
-FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(std::basic_string);
-FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::vector);
-FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::list);
-FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::deque);
-FOLLY_ASSUME_FBVECTOR_COMPATIBLE_4(std::map);
-FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(std::set);
-FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::unique_ptr);
-FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::shared_ptr);
-FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::function);
+// same as `x >= 0`
+template <typename T>
+constexpr bool is_non_negative(T x) {
+  return !x || is_positive(x);
+}
 
-// Boost
-FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(boost::shared_ptr);
+template <typename RHS, RHS rhs, typename LHS>
+bool less_than(LHS const lhs) {
+  return detail::less_than_impl<
+    RHS, rhs, typename std::remove_reference<LHS>::type
+  >(lhs);
+}
 
-#define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, cv_qual) \
-  template <typename TTheClass_, typename RTheReturn_, typename... TTheArgs_> \
-  class classname<TTheClass_, RTheReturn_(TTheArgs_...) cv_qual> { \
-    template < \
-      typename UTheClass_, RTheReturn_ (UTheClass_::*)(TTheArgs_...) cv_qual \
-    > struct sfinae {}; \
-    template <typename UTheClass_> \
-    constexpr static bool test(sfinae<UTheClass_, &UTheClass_::func_name>*) \
-    { return true; } \
-    template <typename> \
-    constexpr static bool test(...) { return false; } \
-  public: \
-    constexpr static bool value = test<TTheClass_>(nullptr); \
-  }
+template <typename RHS, RHS rhs, typename LHS>
+bool greater_than(LHS const lhs) {
+  return detail::greater_than_impl<
+    RHS, rhs, typename std::remove_reference<LHS>::type
+  >(lhs);
+}
+} // namespace folly
 
-/*
- * The FOLLY_CREATE_HAS_MEMBER_FN_TRAITS is used to create traits
- * classes that check for the existence of a member function with
- * a given name and signature. It currently does not support
- * checking for inherited members.
- *
- * Such classes receive two template parameters: the class to be checked
- * and the signature of the member function. A static boolean field
- * named `value` (which is also constexpr) tells whether such member
- * function exists.
- *
- * Each traits class created is bound only to the member name, not to
- * its signature nor to the type of the class containing it.
- *
- * Say you need to know if a given class has a member function named
- * `test` with the following signature:
- *
- *    int test() const;
- *
- * You'd need this macro to create a traits class to check for a member
- * named `test`, and then use this traits class to check for the signature:
- *
- * namespace {
- *
- * FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(has_test_traits, test);
- *
- * } // unnamed-namespace
- *
- * void some_func() {
- *   cout << "Does class Foo have a member int test() const? "
- *     << boolalpha << has_test_traits<Foo, int() const>::value;
- * }
+// Assume nothing when compiling with MSVC.
+#ifndef _MSC_VER
+// gcc-5.0 changed string's implementation in libstdc++ to be non-relocatable
+#if !_GLIBCXX_USE_CXX11_ABI
+FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(std::basic_string)
+#endif
+FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::vector)
+FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::list)
+FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::deque)
+FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::unique_ptr)
+FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::shared_ptr)
+FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::function)
+#endif
+
+/* Some combinations of compilers and C++ libraries make __int128 and
+ * unsigned __int128 available but do not correctly define their standard type
+ * traits.
  *
- * You can use the same traits class to test for a completely different
- * signature, on a completely different class, as long as the member name
- * is the same:
+ * If FOLLY_SUPPLY_MISSING_INT128_TRAITS is defined, we define these traits
+ * here.
  *
- * void some_func() {
- *   cout << "Does class Foo have a member int test()? "
- *     << boolalpha << has_test_traits<Foo, int()>::value;
- *   cout << "Does class Foo have a member int test() const? "
- *     << boolalpha << has_test_traits<Foo, int() const>::value;
- *   cout << "Does class Bar have a member double test(const string&, long)? "
- *     << boolalpha << has_test_traits<Bar, double(const string&, long)>::value;
- * }
+ * @author: Phil Willoughby <philwill@fb.com>
  */
-#define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(classname, func_name) \
-  template <typename, typename> class classname; \
-  FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, ); \
-  FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, const); \
-  FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, volatile); \
-  FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, volatile const)
-
-#endif //FOLLY_BASE_TRAITS_H_
+#if FOLLY_SUPPLY_MISSING_INT128_TRAITS
+FOLLY_NAMESPACE_STD_BEGIN
+template <>
+struct is_arithmetic<__int128> : ::std::true_type {};
+template <>
+struct is_arithmetic<unsigned __int128> : ::std::true_type {};
+template <>
+struct is_integral<__int128> : ::std::true_type {};
+template <>
+struct is_integral<unsigned __int128> : ::std::true_type {};
+template <>
+struct make_unsigned<__int128> {
+  typedef unsigned __int128 type;
+};
+template <>
+struct make_signed<__int128> {
+  typedef __int128 type;
+};
+template <>
+struct make_unsigned<unsigned __int128> {
+  typedef unsigned __int128 type;
+};
+template <>
+struct make_signed<unsigned __int128> {
+  typedef __int128 type;
+};
+template <>
+struct is_signed<__int128> : ::std::true_type {};
+template <>
+struct is_unsigned<unsigned __int128> : ::std::true_type {};
+FOLLY_NAMESPACE_STD_END
+#endif // FOLLY_SUPPLY_MISSING_INT128_TRAITS