You can absolutely use specific return types, even though most examples on the web seems to return the ActionResult. The only time I would return the ActionResult class is when different paths of the action method returns different subtypes. Steven Sanderson also recommends returning specific types in his book Pro ASP.NET MVC Framework. Take a … Read more
The correct way to think about this is to imagine that every class requires its objects to have a certain number of “slots”; those slots are filled with methods. The question “what method actually gets called?” requires you to figure out two things: What are the contents of each slot? Which slot is called? Let’s … Read more
You need to use virtual keyword abstract class Base { // use virtual keyword public virtual int x { get { throw new NotImplementedException(); } } } or define an abstract property: abstract class Base { // use abstract keyword public abstract int x { get; } } and use override keyword when in the … Read more
The instanceof keyword, as described by the other answers, is usually what you would want. Keep in mind that instanceof will return true for superclasses as well. If you want to see if an object is a direct instance of a class, you could compare the class. You can get the class object of an … Read more
The answer is copy semantics. When you pass an object by value in C++, e.g. printArea(Shape shape) a copy is made of the object you pass. And if you pass a derived class to this function, all that’s copied is the base class Shape. If you think about it, there’s no way the compiler could … Read more
I am not going to attempt to answer everything in this question, it is just too large. Having said that here are some observations about the code you posted which might help: The GPU side new operator allocates memory from a private runtime heap. As of CUDA 6, that memory cannot be accessed by the … Read more
There is no polymorphism for fields in Java. There is however, inheritance. What you’ve effectively done is create two fields in your Rectangle class, with the same name. The names of the field are, effectively: public class Rectangle { public int Shape.x; public int Rectangle.x; } The above doesn’t represent valid Java, its just an … Read more
You can’t treat arrays polymorphically, so while new B[100] creates an array of B objects and returns a pointer to the array – or equivalently the first element of the array – and while it is valid to assign this pointer to a pointer to a base class, it is not valid to treat this … Read more
This problem can be reduced to the following simple example (thanks to turbulencetoo): trait Foo {} fn make_dyn<T: Foo + ?Sized>(arg: &T) -> &dyn Foo { arg } At first glance, it really looks like this should compile, as you observed: If T is Sized, the compiler knows statically what vtable it should use to … Read more
You could declare, and implement, a pure virtual destructor: class ShapeF { public: virtual ~ShapeF() = 0; … }; ShapeF::~ShapeF() {} It’s a tiny step from what you already have, and will prevent ShapeF from being instantiated directly. The derived classes won’t need to change.