From 3f62112e3a1b180a9b931d6f43b3cdc74e7ba3b9 Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Mon, 7 Oct 2024 22:03:56 +0200
Subject: option: assignment operator + minor cleanup

---
 option.h       | 37 ++++++++++++++++++++++++++++++++++---
 test/option.cc | 12 ++++++++++++
 2 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/option.h b/option.h
index 20104d7..cd12f88 100644
--- a/option.h
+++ b/option.h
@@ -29,7 +29,7 @@ struct option {
   // -- CONSTRUCTOR - NONE -----------------------------------------------------
 
   constexpr option() = default;
-  constexpr option(none) : option() {}
+  constexpr option(none) noexcept : option() {}
 
   // -- CONSTRUCTOR - VALUE ----------------------------------------------------
 
@@ -47,11 +47,40 @@ struct option {
     }
   }
 
-  template <typename U = T>
-  constexpr option(T&& val) : m_has_value{true} {
+  constexpr option(const T& val) : m_has_value{true} {
+    new (&m_value) T(val);
+  }
+
+  constexpr option(T&& val) noexcept : m_has_value{true} {
     new (&m_value) T(std::move(val));
   }
 
+  // -- ASSIGNMENT -------------------------------------------------------------
+
+  constexpr option& operator=(const option& op) {
+    if (this == &op) {
+      return *this;
+    }
+    reset();
+    if (op.has_value()) {
+      new (&m_value) T(op.value());
+      m_has_value = true;
+    }
+    return *this;
+  }
+
+  constexpr option& operator=(option&& op) noexcept {
+    if (this == &op) {
+      return *this;
+    }
+    reset();
+    if (op.has_value()) {
+      new (&m_value) T(std::move(op.take()));
+      m_has_value = true;
+    }
+    return *this;
+  }
+
   // -- DESTRUCTOR -------------------------------------------------------------
 
   ~option() {
@@ -62,6 +91,8 @@ struct option {
 
   template <typename... Params>
   constexpr T& emplace(Params&&... params) {
+    static_assert(std::is_constructible<T, Params...>::value,
+                  "T not constructible from Params...");
     reset();
     new (&m_value) T(std::forward<Params>(params)...);
     m_has_value = true;
diff --git a/test/option.cc b/test/option.cc
index 09c0fdf..4aa08a1 100644
--- a/test/option.cc
+++ b/test/option.cc
@@ -61,6 +61,18 @@ int main() {
     assert(!o2.has_value());
     assert(o4.has_value());
 
+    option<checker> o5;
+    // copy assign
+    o5 = o4;
+    assert(o4.has_value());
+    assert(o5.has_value());
+
+    option<checker> o6;
+    // move assign
+    o6 = std::move(o5);
+    assert(!o5.has_value());
+    assert(o6.has_value());
+
     // take reference to inner
     auto x = o3.value();
     // take ownership of inner
-- 
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