Make base::Optional constructor constexpr.

base/optional_unittest.cc

Index: base/optional_unittest.cc
diff --git a/base/optional_unittest.cc b/base/optional_unittest.cc
index 565b6cd6c74cad6679c02c68953176b0dce11c6f..4736d5b09de7677e11ddb2e471d4e592586ec397 100644
--- a/base/optional_unittest.cc
+++ b/base/optional_unittest.cc
@@ -96,6 +96,8 @@ static_assert(
     !is_trivially_destructible<Optional<NonTriviallyDestructible>>::value,
     "OptionalIsTriviallyDestructible");
 
+static_assert(!base::Optional<bool>(), "OptionalHasConstexprConstructor");

[danakj, 2016/10/21 21:05:01]

Can you add tests for the other constructors as well that should be constexpr?
http://en.cppreference.com/w/cpp/utility/optional/optional

[alshabalin, 2016/10/21 22:36:05]

Done (partially). Reading http://en.cppreference.com/w/cpp/language/constexpr it
seems that until C++14 constructors of union-like classes cannot be constexpr.
This means that only Optional of types with trivial special member functions can
have constexpr constructors.

+
 TEST(OptionalTest, DefaultConstructor) {
   {
     Optional<float> o;