Reference vs Object vs Types The key, for me, is understanding the difference between an object and its references, or put in other words the difference between an object and its types. When we create an object in Java, we declare its true nature, which will never change (e.g. new Truck()). But any given object … Read more
Let’s take a closer look at your last line, and explode it to see what’s happening: let temporaryAnyObject = test() let temporaryString = temporaryAnyObject as String dict[“test”] = temporaryString The error is on the second line, where you are telling the compiler to enforce that temporaryAnyObject is definitely a String. The code will still compile … Read more
[*] The technical problem is that there’s no way to work out from a Base* what the offset is between the start of the Base sub-object and the start of the Derived object. In your example it appears OK, because there’s only one class in sight with a Base base, and so it appears irrelevant … Read more
If by “illegal” you mean ill-formed, then it is illegal if the base class is inaccessible or ambiguous. It is inaccessible when, for example, the base class is private. class A {}; class B : A {}; … B b; A *pa = &b; // ERROR: base class is inaccessible Note that even in C++11 … Read more
In order to understand the cast system, you need to dive into the object model. The classic representation of a simple hierarchy model is containment: if B derives from A then the B object will, in fact, contain an A subobject alongside its own attributes. With this model downcasting is a simple pointer manipulation by … Read more
This ought to work: if (ptr->IsChildOne()) { SomeClientExpectingAChildOne(std::static_pointer_cast<ChildOne>(ptr)); }
That is correct. When you do that you are casting it it into an employee object, so that means you cannot access anything manager specific. Downcasting is where you take a base class and then try and turn it into a more specific class. This can be accomplished with using is and an explicit cast … Read more
The practical difference is this: var optionalString = dict[“SomeKey”] as? String optionalString will be a variable of type String?. If the underlying type is something other than a String this will harmlessly just assign nil to the optional. var optionalString = dict[“SomeKey”] as! String? This says, I know this thing is a String?. This too … Read more
No. A reference to a derived class must actually refer to an instance of the derived class (or null). Otherwise how would you expect it to behave? For example: object o = new object(); string s = (string) o; int i = s.Length; // What can this sensibly do? If you want to be able … Read more