added missing virtual dtor for callable_base. first working version

Function.hpp

@@ -10,6 +10,8 @@ private:
     {
     public:
         virtual Ret call(Args...) = 0;
+        virtual ~callable_base() {}
+        //virtual ~callable_base() = default;    // melyik számít szebbnek? van bármi különbség?
     };
 
     template <typename Fun>
@@ -19,8 +21,11 @@ private:
         Fun _fun;
     public:
         callable(Fun fun):_fun(fun) {}
-        virtual Ret call(Args... args)
+
+        virtual Ret call(Args... args) override
         { return _fun(std::forward<Args>(args)...); }
+
+        virtual ~callable() override {}
     };
 
     callable_base* _fun;
@@ -37,5 +42,8 @@ public:
     Ret operator()(Args... args) const
     { return _fun->call(std::forward<Args>(args)...); }
 
+    operator bool() const
+    { return static_cast<bool>(_fun); }
+
     ~Function() { delete _fun; }
 };