Downcasting permits an object of a superclass type to be treated as an object of any subclass type.
Questions tagged [downcast]
589 questions
1
vote
1 answer
Java downcast objects invoking sub method
The printout is: Fruit
Apple
Golden
Golden
I want to know why the object c.make() invokes a method in class Golden instead of class Apple.Because I think that c is the object of class Apple, where…
APRIL Paxton
- 15
- 6
1
vote
1 answer
Avoiding downcasts in a Swift 3 completion handler with Google Drive REST API
I'm using the Google Drive REST API in a Swift 3 app. Queries are executed using the executeQuery method of GTLRDriveService. This method takes a completion block of type GTLRServiceCompletionHandler?, which in turn is declared as
public typealias…
Ted Hopp
- 232,168
- 48
- 399
- 521
1
vote
1 answer
Derived class has no extra data members; Is it safe to statically downcast a base object to a derived object?
struct Base {
int i, j;
};
struct Derived : Base {};
With above scenario, if we do following:
Base b;
auto& d = static_cast(b);
d.i = 1;
Will it be an undefined behaviour?
Note: For some reasons, I can't edit the code of an auto…
iammilind
- 68,093
- 33
- 169
- 336
1
vote
2 answers
use `static_cast` for downcasting over a null pointer (single or multiple inheritance)
As the title says, if I cast a pointer to a base class, to a derived class, when the pointer is null, is it a safe operation from the point of view of the C++11/C++14 standard?
struct base
{
virtual ~base() = default;
};
struct derived : base…
ABu
- 10,423
- 6
- 52
- 103
1
vote
2 answers
How to Down Cast an Object in Java
I am working with an API in my company where I would like to create a subclass for an existing object. Here are the caveats:
I cannot modify the superclass
I cannot modify how the superclass object is instantiated
The example I see most commonly…
Jake Fairbairn
- 183
- 3
- 14
1
vote
2 answers
Type casting/Down casting in Java
I'm trying to clarify this so I fully understand type casting. Please correct me on anything that is incorrect as I've been self learning java for about 2 months now at a really slow pace.
Let's say I created a class called SubObject. And I am aware…
simmonson
- 137
- 1
- 9
1
vote
2 answers
Java - Upcasting and Downcasting
I Knew there are plenty of articles/questions in stackoverflow describing about upcasting and downcasting in Java. And I knew what is upcasting and downcasting. But my question is not specfic to that.
Upcasting - Conversion from child to parent -…
Aishu
- 1,310
- 6
- 28
- 52
1
vote
1 answer
Trying to downcast pointer of object in std::vector
In the constructor of one of my classes I have this line :
m_Projects = std::vector(); //m_Projects type is std::vector
m_Current = nullptr; //m_Current type is parent_project*
In a function of this same class I have…
DreamTool
- 149
- 1
- 15
1
vote
1 answer
Why do we need Upcasting & Downcasting in C#?
Consider we are having three classes, Shape which is the base class and two other classes Circle and Text that inherits from the base classe (Shape)
Shape.cs
namespace ObjectOriented
{
public class Shape
{
public int Height { get;…
D.AhmedRafik
- 81
- 2
- 15
1
vote
1 answer
Static Cast from ( Base Reference to Base Object ) to ( Derived Class Reference)
In the main function below , the first static_cast is valid as i am trying to cast a (base class reference to Derived1 class) to a derived reference
But why is the second cast printing with the values, though it prints junk value for d2.y, i assumed…
LearningCpp
- 972
- 12
- 29
1
vote
1 answer
Is it possible to convert instance of a class to an instance of a subclass?
I've recently came across a case where it would be very convenient to convert an instance of a class to a subclass, while the instance has been created within the parent class. But I've never seen such thing. So is there a way to do something…
Guig
- 9,891
- 7
- 64
- 126
1
vote
1 answer
Java Cloning and downcasting
Below is my sample code:
class One implements Cloneable {
@Override
public One clone() throws CloneNotSupportedException {
One obj = (One) super.clone();
return obj;
}
}
public class Two extends One {
@Override
…
Priyatam Roy
- 85
- 9
1
vote
2 answers
C++ : Extend object by downcasting to derived class
I guess this a classic, but in my case I have constraints that should simplify the problem.
It's just that I'm getting some struct A at the input of my module, and want to add a few attributes to it. So I create a struct B which extends A, and add…
Charles
- 988
- 1
- 11
- 28
1
vote
2 answers
How can i call the child method after downcasting parent object to child object?
I have Request class which is a parent class and AddressRequest class which extends Request.
public AddressRequest extends Request
{
private String userId;
public String getUserId() {
return userId;
}
public void…
Anjana Ethilkandy
- 21
- 6
1
vote
1 answer
incorrect type not detected by typescript compiler?
Here is a simple example.
I'm using this kind of design for a MVC architecture: you can think of M (and derived classes) as a model and V (and derived classes) as a view:
abstract class M { abstract update() : void; }
abstract class V { abstract…
D.Fober
- 11
- 2