1 files changed, 50 insertions, 14 deletions

diff --git a/include/ftl/optional.h b/include/ftl/optional.h
index daf4502bd2..626507fd8f 100644
--- a/include/ftl/optional.h
+++ b/include/ftl/optional.h
@@ -18,9 +18,10 @@
 
 #include <functional>
 #include <optional>
-#include <type_traits>
 #include <utility>
 
+#include <ftl/details/optional.h>
+
 namespace android::ftl {
 
 // Superset of std::optional<T> with monadic operations, as proposed in https://wg21.link/P0798R8.
@@ -31,41 +32,76 @@ template <typename T>
 struct Optional final : std::optional<T> {
   using std::optional<T>::optional;
 
+  // Implicit downcast.
+  Optional(std::optional<T> other) : std::optional<T>(std::move(other)) {}
+
   using std::optional<T>::has_value;
   using std::optional<T>::value;
 
   // Returns Optional<U> where F is a function that maps T to U.
   template <typename F>
   constexpr auto transform(F&& f) const& {
-    using U = std::remove_cv_t<std::invoke_result_t<F, decltype(value())>>;
-    if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), value()));
-    return Optional<U>();
+    using R = details::transform_result_t<F, decltype(value())>;
+    if (has_value()) return R(std::invoke(std::forward<F>(f), value()));
+    return R();
   }
 
   template <typename F>
   constexpr auto transform(F&& f) & {
-    using U = std::remove_cv_t<std::invoke_result_t<F, decltype(value())>>;
-    if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), value()));
-    return Optional<U>();
+    using R = details::transform_result_t<F, decltype(value())>;
+    if (has_value()) return R(std::invoke(std::forward<F>(f), value()));
+    return R();
   }
 
   template <typename F>
   constexpr auto transform(F&& f) const&& {
-    using U = std::invoke_result_t<F, decltype(std::move(value()))>;
-    if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), std::move(value())));
-    return Optional<U>();
+    using R = details::transform_result_t<F, decltype(std::move(value()))>;
+    if (has_value()) return R(std::invoke(std::forward<F>(f), std::move(value())));
+    return R();
   }
 
   template <typename F>
   constexpr auto transform(F&& f) && {
-    using U = std::invoke_result_t<F, decltype(std::move(value()))>;
-    if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), std::move(value())));
-    return Optional<U>();
+    using R = details::transform_result_t<F, decltype(std::move(value()))>;
+    if (has_value()) return R(std::invoke(std::forward<F>(f), std::move(value())));
+    return R();
+  }
+
+  // Returns Optional<U> where F is a function that maps T to Optional<U>.
+  template <typename F>
+  constexpr auto and_then(F&& f) const& {
+    using R = details::and_then_result_t<F, decltype(value())>;
+    if (has_value()) return std::invoke(std::forward<F>(f), value());
+    return R();
+  }
+
+  template <typename F>
+  constexpr auto and_then(F&& f) & {
+    using R = details::and_then_result_t<F, decltype(value())>;
+    if (has_value()) return std::invoke(std::forward<F>(f), value());
+    return R();
+  }
+
+  template <typename F>
+  constexpr auto and_then(F&& f) const&& {
+    using R = details::and_then_result_t<F, decltype(std::move(value()))>;
+    if (has_value()) return std::invoke(std::forward<F>(f), std::move(value()));
+    return R();
+  }
+
+  template <typename F>
+  constexpr auto and_then(F&& f) && {
+    using R = details::and_then_result_t<F, decltype(std::move(value()))>;
+    if (has_value()) return std::invoke(std::forward<F>(f), std::move(value()));
+    return R();
   }
 };
 
-// Deduction guide.
+// Deduction guides.
 template <typename T>
 Optional(T) -> Optional<T>;
 
+template <typename T>
+Optional(std::optional<T>) -> Optional<T>;
+
 }  // namespace android::ftl