Harden failure signal handler in the face of memory corruptions

[folly.git] / folly / Traits.h

diff --git a/folly/Traits.h b/folly/Traits.h
index d2fad50ee842d3be52c9881bc5bbd32da96db52c..966dcc578f7355e33cf8e8477c86f70dc67a3d24 100644 (file)
--- a/folly/Traits.h
+++ b/folly/Traits.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 Facebook, Inc.
+ * Copyright 2014 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,9 +20,21 @@
 #define FOLLY_BASE_TRAITS_H_
 
 #include <memory>
+#include <limits>
 #include <type_traits>
 
+#include "folly/Portability.h"
+
+// libc++ doesn't provide this header
+#if !FOLLY_USE_LIBCPP
+// 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>
@@ -222,7 +234,7 @@ 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;
@@ -246,7 +258,7 @@ template <class K, class V, class C, class A>
 template <class T>
   class shared_ptr;
 
-}
+FOLLY_NAMESPACE_STD_END
 
 namespace boost {
 
@@ -277,14 +289,160 @@ struct IsOneOf<T, T1, Ts...> {
   enum { value = std::is_same<T, T1>::value || IsOneOf<T, Ts...>::value };
 };
 
+/**
+ * A traits class to check for incomplete types.
+ *
+ * Example:
+ *
+ *  struct FullyDeclared {}; // complete type
+ *  struct ForwardDeclared; // incomplete type
+ *
+ *  is_complete<int>::value // evaluates to true
+ *  is_complete<FullyDeclared>::value // evaluates to true
+ *  is_complete<ForwardDeclared>::value // evaluates to false
+ *
+ *  struct ForwardDeclared {}; // declared, at last
+ *
+ *  is_complete<ForwardDeclared>::value // now it evaluates to true
+ *
+ * @author: Marcelo Juchem <marcelo@fb.com>
+ */
+template <typename T>
+class is_complete {
+  template <unsigned long long> struct sfinae {};
+  template <typename U>
+  constexpr static bool test(sfinae<sizeof(U)>*) { return true; }
+  template <typename> constexpr static bool test(...) { return false; }
+public:
+  constexpr static bool value = test<T>(nullptr);
+};
+
+/*
+ * Complementary type traits for integral comparisons.
+ *
+ * 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 {
+
+template <typename T, bool>
+struct is_negative_impl {
+  constexpr static bool check(T x) { return x < 0; }
+};
+
+template <typename T>
+struct is_negative_impl<T, false> {
+  constexpr static bool check(T x) { return false; }
+};
+
+template <typename RHS, RHS rhs, typename LHS>
+bool less_than_impl(
+  typename std::enable_if<
+    (rhs <= std::numeric_limits<LHS>::max()
+      && rhs > std::numeric_limits<LHS>::min()),
+    LHS
+  >::type const lhs
+) {
+  return lhs < rhs;
+}
+
+template <typename RHS, RHS rhs, typename LHS>
+bool less_than_impl(
+  typename std::enable_if<
+    (rhs > std::numeric_limits<LHS>::max()),
+    LHS
+  >::type const
+) {
+  return true;
+}
+
+template <typename RHS, RHS rhs, typename LHS>
+bool less_than_impl(
+  typename std::enable_if<
+    (rhs <= std::numeric_limits<LHS>::min()),
+    LHS
+  >::type const
+) {
+  return false;
+}
+
+template <typename RHS, RHS rhs, typename LHS>
+bool greater_than_impl(
+  typename std::enable_if<
+    (rhs <= std::numeric_limits<LHS>::max()
+      && rhs >= std::numeric_limits<LHS>::min()),
+    LHS
+  >::type const lhs
+) {
+  return lhs > rhs;
+}
+
+template <typename RHS, RHS rhs, typename LHS>
+bool greater_than_impl(
+  typename std::enable_if<
+    (rhs > std::numeric_limits<LHS>::max()),
+    LHS
+  >::type const
+) {
+  return false;
+}
+
+template <typename RHS, RHS rhs, typename LHS>
+bool greater_than_impl(
+  typename std::enable_if<
+    (rhs < std::numeric_limits<LHS>::min()),
+    LHS
+  >::type const
+) {
+  return true;
+}
+
+} // namespace detail {
+
+// same as `x < 0`
+template <typename T>
+constexpr bool is_negative(T x) {
+  return folly::detail::is_negative_impl<T, std::is_signed<T>::value>::check(x);
+}
+
+// same as `x <= 0`
+template <typename T>
+constexpr bool is_non_positive(T x) { return !x || folly::is_negative(x); }
+
+// same as `x > 0`
+template <typename T>
+constexpr bool is_positive(T x) { return !is_non_positive(x); }
+
+// same as `x >= 0`
+template <typename T>
+constexpr bool is_non_negative(T x) {
+  return !x || is_positive(x);
+}
+
+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);
+}
+
+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
 
 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);
@@ -352,6 +510,8 @@ FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(boost::shared_ptr);
  *   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> class classname; \