From 0df06afe8dc385f970038aa18876b8d573108983 Mon Sep 17 00:00:00 2001
From: Simon Brand <simon@codeplay.com>
Date: Tue, 24 Oct 2017 15:32:22 +0100
Subject: [PATCH] Fix #2

---
 optional.hpp         | 71 +++++++++++++++++++++++++++++++++++++++-----
 tests/extensions.cpp | 13 ++++++--
 2 files changed, 74 insertions(+), 10 deletions(-)

diff --git a/optional.hpp b/optional.hpp
index 3830f9a..9f768b2 100644
--- a/optional.hpp
+++ b/optional.hpp
@@ -337,6 +337,60 @@ template <class T> class optional : private detail::optional_storage_base<T> {
   using base = detail::optional_storage_base<T>;
 
 public:
+#ifdef TL_OPTIONAL_CXX14
+  /// \group and_then
+  /// Carries out some operation which returns an optional on the stored object
+  /// if there is one. \requires `std::invoke(std::forward<F>(f), value())`
+  /// returns a `std::optional<U>` for some `U`. \returns Let `U` be the result
+  /// of `std::invoke(std::forward<F>(f), value())`. Returns a
+  /// `std::optional<U>`. The return value is empty if `*this` is empty,
+  /// otherwise the return value of `std::invoke(std::forward<F>(f), value())`
+  /// is returned. \group and_then \synopsis template <class F>\nconstexpr auto
+  /// and_then(F &&f) &;
+  template <class F> TL_OPTIONAL_11_CONSTEXPR auto and_then(F &&f) & {
+    using result = detail::invoke_result_t<F, T &>;
+    static_assert(detail::is_optional<result>::value,
+                  "F must return an optional");
+
+    return has_value() ? detail::invoke(std::forward<F>(f), **this)
+                       : result(nullopt);
+  }
+
+  /// \group and_then
+  /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) &&;
+  template <class F> TL_OPTIONAL_11_CONSTEXPR auto and_then(F &&f) && {
+    using result = detail::invoke_result_t<F, T &&>;
+    static_assert(detail::is_optional<result>::value,
+                  "F must return an optional");
+
+    return has_value() ? detail::invoke(std::forward<F>(f), std::move(**this))
+                       : result(nullopt);
+  }
+
+  /// \group and_then
+  /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &;
+  template <class F> constexpr auto and_then(F &&f) const & {
+    using result = detail::invoke_result_t<F, const T &>;
+    static_assert(detail::is_optional<result>::value,
+                  "F must return an optional");
+
+    return has_value() ? detail::invoke(std::forward<F>(f), **this)
+                       : result(nullopt);
+  }
+
+#ifndef TL_OPTIONAL_NO_CONSTRR
+  /// \group and_then
+  /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &&;
+  template <class F> constexpr auto and_then(F &&f) const && {
+    using result = detail::invoke_result_t<F, const T &&>;
+    static_assert(detail::is_optional<result>::value,
+                  "F must return an optional");
+
+    return has_value() ? detail::invoke(std::forward<F>(f), std::move(**this))
+                       : result(nullopt);
+  }
+#endif
+#else
   /// \group and_then
   /// Carries out some operation which returns an optional on the stored object
   /// if there is one. \requires `std::invoke(std::forward<F>(f), value())`
@@ -347,8 +401,8 @@ public:
   /// is returned. \group and_then \synopsis template <class F>\nconstexpr auto
   /// and_then(F &&f) &;
   template <class F>
-  TL_OPTIONAL_11_CONSTEXPR detail::invoke_result_t<F, T> and_then(F &&f) & {
-    using result = detail::invoke_result_t<F, T>;
+  TL_OPTIONAL_11_CONSTEXPR detail::invoke_result_t<F, T &> and_then(F &&f) & {
+    using result = detail::invoke_result_t<F, T &>;
     static_assert(detail::is_optional<result>::value,
                   "F must return an optional");
 
@@ -359,8 +413,8 @@ public:
   /// \group and_then
   /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) &&;
   template <class F>
-  TL_OPTIONAL_11_CONSTEXPR detail::invoke_result_t<F, T> and_then(F &&f) && {
-    using result = detail::invoke_result_t<F, T>;
+  TL_OPTIONAL_11_CONSTEXPR detail::invoke_result_t<F, T &&> and_then(F &&f) && {
+    using result = detail::invoke_result_t<F, T &&>;
     static_assert(detail::is_optional<result>::value,
                   "F must return an optional");
 
@@ -371,8 +425,8 @@ public:
   /// \group and_then
   /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &;
   template <class F>
-  constexpr detail::invoke_result_t<F, T> and_then(F &&f) const & {
-    using result = detail::invoke_result_t<F, T>;
+  constexpr detail::invoke_result_t<F, const T &> and_then(F &&f) const & {
+    using result = detail::invoke_result_t<F, const T &>;
     static_assert(detail::is_optional<result>::value,
                   "F must return an optional");
 
@@ -384,8 +438,8 @@ public:
   /// \group and_then
   /// \synopsis template <class F>\nconstexpr auto and_then(F &&f) const &&;
   template <class F>
-  constexpr detail::invoke_result_t<F, T> and_then(F &&f) const && {
-    using result = detail::invoke_result_t<F, T>;
+  constexpr detail::invoke_result_t<F, const T &&> and_then(F &&f) const && {
+    using result = detail::invoke_result_t<F, const T &&>;
     static_assert(detail::is_optional<result>::value,
                   "F must return an optional");
 
@@ -393,6 +447,7 @@ public:
                        : result(nullopt);
   }
 #endif
+#endif
 
 #ifdef TL_OPTIONAL_CXX14
   /// \brief Carries out some operation on the stored object if there is one.
diff --git a/tests/extensions.cpp b/tests/extensions.cpp
index 2ef9bce..71a5e8f 100644
--- a/tests/extensions.cpp
+++ b/tests/extensions.cpp
@@ -335,11 +335,20 @@ TEST_CASE("Monadic operations", "[monadic]") {
   };
 
 #ifdef TL_OPTIONAL_CXX14
-  // Reported by Mark Papadakis
-  SECTION("map const correctness") {
+  SECTION("Issue #1") {
     tl::optional<foo> f = foo{};
     auto l = [](auto &&x) { x.non_const(); };
     f.map(l);
   }
 #endif
+
+  struct overloaded {
+    tl::optional<int> operator()(foo &) { return 0; }
+    tl::optional<std::string> operator()(const foo &) { return ""; }
+  };
+
+  SECTION("Issue #2") {
+    tl::optional<foo> f = foo{};
+    auto x = f.and_then(overloaded{});
+  }
 };