From 084a9001f4e8bdb0fc257d772bf03621c9ee3260 Mon Sep 17 00:00:00 2001
From: Deniz Evrenci <denizevrenci@gmail.com>
Date: Mon, 8 Jul 2019 19:35:48 +0900
Subject: [PATCH 1/3] Add missing noexcept specifications to methods of
 optional<T&>

---
 include/tl/optional.hpp | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/include/tl/optional.hpp b/include/tl/optional.hpp
index 4d41e54..9cba0b8 100644
--- a/include/tl/optional.hpp
+++ b/include/tl/optional.hpp
@@ -1939,12 +1939,12 @@ public:
   template <class U = T,
             detail::enable_if_t<!detail::is_optional<detail::decay_t<U>>::value>
                 * = nullptr>
-  constexpr optional(U &&u) : m_value(std::addressof(u)) {
+  constexpr optional(U &&u)  noexcept : m_value(std::addressof(u)) {
     static_assert(std::is_lvalue_reference<U>::value, "U must be an lvalue");
   }
 
   template <class U>
-  constexpr explicit optional(const optional<U> &rhs) : optional(*rhs) {}
+  constexpr explicit optional(const optional<U> &rhs) noexcept : optional(*rhs) {}
 
   /// No-op
   ~optional() = default;
@@ -1977,7 +1977,7 @@ public:
   ///
   /// Rebinds this optional to the referee of `rhs` if there is one. Otherwise
   /// resets the stored value in `*this`.
-  template <class U> optional &operator=(const optional<U> &rhs) {
+  template <class U> optional &operator=(const optional<U> &rhs) noexcept {
     m_value = std::addressof(rhs.value());
     return *this;
   }
@@ -1996,14 +1996,14 @@ public:
   void swap(optional &rhs) noexcept { std::swap(m_value, rhs.m_value); }
 
   /// Returns a pointer to the stored value
-  constexpr const T *operator->() const { return m_value; }
+  constexpr const T *operator->() const noexcept { return m_value; }
 
-  TL_OPTIONAL_11_CONSTEXPR T *operator->() { return m_value; }
+  TL_OPTIONAL_11_CONSTEXPR T *operator->() noexcept { return m_value; }
 
   /// Returns the stored value
-  TL_OPTIONAL_11_CONSTEXPR T &operator*() { return *m_value; }
+  TL_OPTIONAL_11_CONSTEXPR T &operator*() noexcept { return *m_value; }
 
-  constexpr const T &operator*() const { return *m_value; }
+  constexpr const T &operator*() const noexcept { return *m_value; }
 
   constexpr bool has_value() const noexcept { return m_value != nullptr; }
 
@@ -2024,7 +2024,7 @@ public:
   }
 
   /// Returns the stored value if there is one, otherwise returns `u`
-  template <class U> constexpr T value_or(U &&u) const & {
+  template <class U> constexpr T value_or(U &&u) const & noexcept {
     static_assert(std::is_copy_constructible<T>::value &&
                       std::is_convertible<U &&, T>::value,
                   "T must be copy constructible and convertible from U");
@@ -2032,7 +2032,7 @@ public:
   }
 
   /// \group value_or
-  template <class U> TL_OPTIONAL_11_CONSTEXPR T value_or(U &&u) && {
+  template <class U> TL_OPTIONAL_11_CONSTEXPR T value_or(U &&u) && noexcept {
     static_assert(std::is_move_constructible<T>::value &&
                       std::is_convertible<U &&, T>::value,
                   "T must be move constructible and convertible from U");

From b074bee4096ef174c5f966fa4a6e046dad956c0d Mon Sep 17 00:00:00 2001
From: Deniz Evrenci <denizevrenci@gmail.com>
Date: Mon, 8 Jul 2019 19:32:17 +0900
Subject: [PATCH 2/3] Fix implementation of optional<T&>::emplace()

---
 include/tl/optional.hpp | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/include/tl/optional.hpp b/include/tl/optional.hpp
index 9cba0b8..ad8ae2f 100644
--- a/include/tl/optional.hpp
+++ b/include/tl/optional.hpp
@@ -1982,15 +1982,12 @@ public:
     return *this;
   }
 
-  /// Constructs the value in-place, destroying the current one if there is
-  /// one.
-  template <class... Args> T &emplace(Args &&... args) noexcept {
-    static_assert(std::is_constructible<T, Args &&...>::value,
-                  "T must be constructible with Args");
-
-    *this = nullopt;
-    this->construct(std::forward<Args>(args)...);
-    return value();
+  /// Rebinds this optional to `u`.
+  template <class U = T,
+            detail::enable_if_t<!detail::is_optional<detail::decay_t<U>>::value>
+                * = nullptr>
+  optional &emplace(U &&u) noexcept {
+    return *this = std::forward<U>(u);
   }
 
   void swap(optional &rhs) noexcept { std::swap(m_value, rhs.m_value); }

From ce266d52807c0d9d78d946c86267422193c6dd11 Mon Sep 17 00:00:00 2001
From: Simon Brand <tartanllama@gmail.com>
Date: Mon, 8 Jul 2019 11:49:21 +0100
Subject: [PATCH 3/3] Add test

---
 tests/issues.cpp | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tests/issues.cpp b/tests/issues.cpp
index d5672a3..1f465e1 100644
--- a/tests/issues.cpp
+++ b/tests/issues.cpp
@@ -31,4 +31,15 @@ TEST_CASE("issue 15") {
 
     o = o;
     REQUIRE(o->value == 42);
+}
+
+TEST_CASE("issue 33") {
+    int i = 0;
+    int j = 0;
+    tl::optional<int&> a = i;
+    a.emplace(j);
+    *a = 42;
+    REQUIRE(j == 42);
+    REQUIRE(*a == 42);
+    REQUIRE(a.has_value());
 }
\ No newline at end of file