Use = default for virtual constructors.

src/muz/base/dl_context.cpp

@@ -53,7 +53,7 @@ namespace datalog {
                 m_limited_size = ctx.get_decl_util().try_get_size(s, m_size);
         }
     public:
-        virtual ~sort_domain() {}
+        virtual ~sort_domain() = default;
 
         sort_kind get_kind() const { return m_kind; }
         virtual unsigned get_constant_count() const = 0;

src/muz/base/dl_engine_base.h

@@ -42,7 +42,7 @@ namespace datalog {
         std::string m_name;
     public:
         engine_base(ast_manager& m, char const* name): m(m), m_name(name) {}
-        virtual ~engine_base() {}
+        virtual ~engine_base() = default;
 
         virtual expr_ref get_answer() = 0;
         virtual expr_ref get_ground_sat_answer () {

src/muz/base/dl_rule_transformer.h

@@ -89,7 +89,7 @@ namespace datalog {
             m_can_destratify_negation(can_destratify_negation), m_transformer(nullptr) {}
 
     public:
-        virtual ~plugin() {}
+        virtual ~plugin() = default;
 
         unsigned get_priority() { return m_priority; }
         bool can_destratify_negation() const { return m_can_destratify_negation; }