ZValElement: Implement move assignment operator

src/Val.cc

@@ -4238,6 +4238,19 @@ TEST_CASE("assignment") {
     CHECK(v2->RefCnt() == 3);
 }
 
+TEST_CASE("move assignment") {
+    auto t = zeek::id::find_type<zeek::RecordType>("conn_id_ctx");
+    auto v1 = zeek::make_intrusive<zeek::RecordVal>(t);
+    auto v2 = zeek::make_intrusive<zeek::RecordVal>(t);
+
+    zeek::ZValElement element1 = zeek::ZValElement(v1, t);
+    CHECK(v1->RefCnt() == 2);            // v1 and element1
+    element1 = zeek::ZValElement(v2, t); // Should use move assignment.
+
+    CHECK(v1->RefCnt() == 1); // Only v1 holds the ref.
+    CHECK(v2->RefCnt() == 2); // v1 and element1 adopted ref from temporary.
+}
+
 TEST_CASE("copy constructor") {
     auto t = zeek::id::find_type<zeek::RecordType>("conn_id_ctx");
     auto v = zeek::make_intrusive<zeek::RecordVal>(t);

src/Val.h

@@ -1198,6 +1198,30 @@ public:
         return *this;
     }
 
+    /**
+     * Move assignment operator.
+     *
+     * Adopts the reference if \a o holds a managed ZVal.
+     */
+    ZValElement& operator=(ZValElement&& o) noexcept {
+        if ( this == &o )
+            return *this;
+
+        if ( is_set && is_managed )
+            Unref(zval.ManagedVal());
+
+        is_set = o.is_set;
+        is_managed = o.is_managed;
+        tag = o.tag;
+        zval = o.zval; // Adopts the reference.
+
+        // Keep is_managed and tag members valid.
+        o.is_set = false;
+        o.zval = ZVal();
+
+        return *this;
+    }
+
     /**
      * Assign a ZVal to ZValElement.
      *