From 247677394ffe662eb3b6afe1a82f65873eea5e4b Mon Sep 17 00:00:00 2001
From: Simon Brand <tartanllama@gmail.com>
Date: Tue, 5 Dec 2017 19:51:20 +0000
Subject: [PATCH] Support mapping functions which return references

---
 optional.hpp         | 6 +++---
 tests/extensions.cpp | 6 ++++++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/optional.hpp b/optional.hpp
index 902d6fe..9629d9b 100644
--- a/optional.hpp
+++ b/optional.hpp
@@ -1595,7 +1595,7 @@ template <class Opt, class F,
 constexpr auto map_impl(Opt &&opt, F &&f) {
   return opt.has_value()
              ? detail::invoke(std::forward<F>(f), *std::forward<Opt>(opt))
-             : optional<Ret>(nullopt);
+             : optional<detail::decay_t<Ret>>(nullopt);
 }
 
 template <class Opt, class F,
@@ -1616,10 +1616,10 @@ template <class Opt, class F,
                                               *std::declval<Opt>())),
           detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
 
-constexpr auto map_impl(Opt &&opt, F &&f) -> optional<Ret> {
+constexpr auto map_impl(Opt &&opt, F &&f) -> optional<detail::decay_t<Ret>> {
   return opt.has_value()
              ? detail::invoke(std::forward<F>(f), *std::forward<Opt>(opt))
-             : optional<Ret>(nullopt);
+             : optional<detail::decay_t<Ret>>(nullopt);
 }
 
 template <class Opt, class F,
diff --git a/tests/extensions.cpp b/tests/extensions.cpp
index 12c45d4..83b2c1d 100644
--- a/tests/extensions.cpp
+++ b/tests/extensions.cpp
@@ -119,6 +119,12 @@ TEST_CASE("Monadic operations", "[monadic]") {
     const tl::optional<int> o37 = tl::nullopt;
     auto o37r = std::move(o37).map([](int) { return; });
     REQUIRE(!o37r);
+
+    // callable which returns a reference
+    tl::optional<int> o38 = 42;
+    auto o38r = o38.map([](int& i) -> const int& { return i; });
+    REQUIRE(o38r);
+    REQUIRE(*o38r == 42);
   }
 
   SECTION("map constexpr") {