cast: disable invalid overloads of known using sfinae

cast.hpp

@@ -127,22 +127,28 @@ namespace cruft::cast {
     /// assert if the value is not a pointer to a subclass of T, else return
     /// the converted value. Note: this is only a debug-time check and is
     /// compiled out in optimised builds.
-    template <typename T, typename V>
-    T*
-    known (V *v)
+    template <
+        typename T,
+        typename V
+    >
+    std::enable_if_t<std::is_pointer_v<T>,T>
+    known (V *const v)
     {
-        CHECK (dynamic_cast<T*> (v));
-        return static_cast<T*> (v);
+        CHECK (dynamic_cast<T> (v));
+        return static_cast<T> (v);
     }
 
 
     //-------------------------------------------------------------------------
-    template <typename T, typename V>
-    T&
+    template <
+        typename T,
+        typename V
+    >
+    std::enable_if_t<std::is_reference_v<T>, T>
     known (V &v)
     {
         CHECK_NOTHROW (dynamic_cast<T> (v));
-        return static_cast<T> (v);
+        return reinterpret_cast<T> (v);
     }