Add Optional::value_type

Summary: Comes in handy, and std::experimental::optional has it.

Reviewed By: yfeldblum

Differential Revision: D2708324

fb-gh-sync-id: 87cdf2449f356d3baf9fb56a608e9c43d8fe79ae

diff --git a/folly/Optional.h b/folly/Optional.h
index 84f5d4439ea1300efda80d342ff5b35009dade31..1832009054bb3a42ea71981837083dc20f7e15d7 100644 (file)
--- a/folly/Optional.h
+++ b/folly/Optional.h
@@ -91,6 +91,8 @@ class OptionalEmptyException : public std::runtime_error {
 template<class Value>
 class Optional {
  public:
+  typedef Value value_type;
+
   static_assert(!std::is_reference<Value>::value,
                 "Optional may not be used with reference types");
   static_assert(!std::is_abstract<Value>::value,