Squashed 'third_party/optional/' content from commit 1baad184f

Change-Id: I9b2473a84dcf6d9892f1f7a9fd21b340796b6ff5
git-subtree-dir: third_party/optional
git-subtree-split: 1baad184f022a3a7502db094a984a86adedf9626
diff --git a/tests/observers.cpp b/tests/observers.cpp
new file mode 100644
index 0000000..642b9f6
--- /dev/null
+++ b/tests/observers.cpp
@@ -0,0 +1,35 @@
+#include "catch.hpp"
+#include "optional.hpp"
+
+struct move_detector {
+  move_detector() = default;
+  move_detector(move_detector &&rhs) { rhs.been_moved = true; }
+  bool been_moved = false;
+};
+
+TEST_CASE("Observers", "[observers]") {
+  tl::optional<int> o1 = 42;
+  tl::optional<int> o2;
+  const tl::optional<int> o3 = 42;
+
+  REQUIRE(*o1 == 42);
+  REQUIRE(*o1 == o1.value());
+  REQUIRE(o2.value_or(42) == 42);
+  REQUIRE(o3.value() == 42);
+  auto success = std::is_same<decltype(o1.value()), int &>::value;
+  REQUIRE(success);
+  success = std::is_same<decltype(o3.value()), const int &>::value;
+  REQUIRE(success);
+  success = std::is_same<decltype(std::move(o1).value()), int &&>::value;
+  REQUIRE(success);
+
+  #ifndef TL_OPTIONAL_NO_CONSTRR
+  success = std::is_same<decltype(std::move(o3).value()), const int &&>::value;
+  REQUIRE(success);
+  #endif
+
+  tl::optional<move_detector> o4{tl::in_place};
+  move_detector o5 = std::move(o4).value();
+  REQUIRE(o4->been_moved);
+  REQUIRE(!o5.been_moved);
+}