cpp: Fix evmc::result's move assignment operator

CHANGELOG.md

@@ -3,7 +3,9 @@
 ## [6.2.2] - unreleased
 
 - Fixed: [[#281](https://github.com/ethereum/evmc/pull/281)]
-  Compilation error of evmc::result::raw() in Visual Studio fixed.
+  Compilation error of `evmc::result::raw()` in Visual Studio fixed.
+- Fixed: [[#282](https://github.com/ethereum/evmc/pull/282)]
+  The `evmc::result`'s move assignment operator fixed.
 
 ## [6.2.1] - 2019-04-29
 

include/evmc/evmc.hpp

@@ -39,16 +39,20 @@ class result : private evmc_result
     /// Move constructor.
     result(result&& other) noexcept : evmc_result{other}
     {
-        // Disable releaser of the rvalue object.
-        other.release = nullptr;
+        other.release = nullptr;  // Disable releasing of the rvalue object.
     }
 
-    result(result const&) = delete;
-
-    /// Move-and-swap assignment operator.
-    result& operator=(result other) noexcept
+    /// Move assignment operator.
+    ///
+    /// The self-assigment MUST never happen.
+    ///
+    /// @param other The other result object.
+    /// @return      The reference to the left-hand side object.
+    result& operator=(result&& other) noexcept
     {
-        std::swap(*this, other);
+        this->~result();                           // Release this object.
+        static_cast<evmc_result&>(*this) = other;  // Copy data.
+        other.release = nullptr;                   // Disable releasing of the rvalue object.
         return *this;
     }
 

test/unittests/test_cpp.cpp

@@ -161,3 +161,40 @@ TEST(cpp, result_raii)
     }
     EXPECT_EQ(release_called, 1);
 }
+
+TEST(cpp, result_move)
+{
+    static auto release_called = 0;
+    auto release_fn = [](const evmc_result*) noexcept { ++release_called; };
+
+    release_called = 0;
+    {
+        auto raw = evmc_result{};
+        raw.gas_left = -1;
+        raw.release = release_fn;
+
+        auto r0 = evmc::result{raw};
+        EXPECT_EQ(r0.gas_left, raw.gas_left);
+
+        auto r1 = std::move(r0);
+        EXPECT_EQ(r1.gas_left, raw.gas_left);
+    }
+    EXPECT_EQ(release_called, 1);
+
+    release_called = 0;
+    {
+        auto raw1 = evmc_result{};
+        raw1.gas_left = 1;
+        raw1.release = release_fn;
+
+        auto raw2 = evmc_result{};
+        raw2.gas_left = 1;
+        raw2.release = release_fn;
+
+        auto r1 = evmc::result{raw1};
+        auto r2 = evmc::result{raw2};
+
+        r2 = std::move(r1);
+    }
+    EXPECT_EQ(release_called, 2);
+}