X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=folly%2FUtility.h;h=4d6725d7070ec70e9684d19db915100c6fc5e9cc;hb=55791684950381d92cef305d1e9124120b178ad5;hp=385ed34ac7d52b5329df8dc59aecc23400b4c4c9;hpb=3cec19d4760d9b4057c7e4a6464be86aad216a73;p=folly.git

diff --git a/folly/Utility.h b/folly/Utility.h
index 385ed34a..4d6725d7 100644
--- a/folly/Utility.h
+++ b/folly/Utility.h
@@ -16,6 +16,7 @@
 
 #pragma once
 
+#include <cstdint>
 #include <type_traits>
 #include <utility>
 
@@ -83,7 +84,7 @@ constexpr typename std::decay<T>::type copy(T&& value) noexcept(
  */
 #if __cpp_lib_as_const || _MSC_VER
 
-/* using override */ using std::as_const
+/* using override */ using std::as_const;
 
 #else
 
@@ -96,4 +97,65 @@ template <class T>
 void as_const(T const&&) = delete;
 
 #endif
+
+#if __cpp_lib_integer_sequence || _MSC_VER
+
+/* using override */ using std::integer_sequence;
+/* using override */ using std::index_sequence;
+/* using override */ using std::make_index_sequence;
+
+#else
+
+template <class T, T... Ints>
+struct integer_sequence {
+  using value_type = T;
+
+  static constexpr std::size_t size() noexcept {
+    return sizeof...(Ints);
+  }
+};
+
+template <std::size_t... Ints>
+using index_sequence = folly::integer_sequence<std::size_t, Ints...>;
+
+namespace detail {
+template <std::size_t N, std::size_t... Ints>
+struct make_index_sequence
+    : detail::make_index_sequence<N - 1, N - 1, Ints...> {};
+
+template <std::size_t... Ints>
+struct make_index_sequence<0, Ints...> : folly::index_sequence<Ints...> {};
+}
+
+template <std::size_t N>
+using make_index_sequence = detail::make_index_sequence<N>;
+
+#endif
+
+/**
+ * A simple function object that passes its argument through unchanged.
+ *
+ * Example:
+ *
+ *   int i = 42;
+ *   int &j = Identity()(i);
+ *   assert(&i == &j);
+ *
+ * Warning: passing a prvalue through Identity turns it into an xvalue,
+ * which can effect whether lifetime extension occurs or not. For instance:
+ *
+ *   auto&& x = std::make_unique<int>(42);
+ *   cout << *x ; // OK, x refers to a valid unique_ptr.
+ *
+ *   auto&& y = Identity()(std::make_unique<int>(42));
+ *   cout << *y ; // ERROR: y did not lifetime-extend the unique_ptr. It
+ *                // is no longer valid
+ */
+struct Identity {
+  using is_transparent = void;
+  template <class T>
+  constexpr T&& operator()(T&& x) const noexcept {
+    return static_cast<T&&>(x);
+  }
+};
 }