Downcasting permits an object of a superclass type to be treated as an object of any subclass type.
Questions tagged [downcast]
589 questions
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Why static casting Derived to Base with private inheritance causes a conversion between "const Derived" to "const Base"?
class Base {
};
class Derived: private Base {
};
int main() {
Derived d;
static_cast
TYeung
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Interface Downcasting
Please suppose I have the following extension method in order to be able to force evaluation of an IEnumerable:
public static List EvaluateNow(this IEnumerable collection)
{
if (collection == null)
{
throw new…
DotNetStudent
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Java upcasting and downcasting problem as follow
I got confused, as the answer suggested option A.
Shouldn't aVehicle bound be viewed as a Vehicle object since the first line operated upcasting?
The question as follow:
Consider the following code snippet:
Vehicle aVehicle = new…
YI Chen Wang
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How do CLR Enumerables downcast Generics
... and can I do it?
So I wanted to implement an EnumerableSubset class for dealing with pagination results within the API:
public interface IEnumerableSubset : IEnumerable{
int Total {get;}
}
public class ListSubset : List,…
GreysonTyrus
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Can't downcast from &mut Box as &mut dyn Any?
I encountered this issue, and I'm wondering why it doesn't work.
I managed to replicate the problem :
I'm trying to get back to the struct from &mut Box, and this is my go at it:
use std::any::Any;
trait A {}
struct B;
impl A for B…
LucioleMaléfique
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Is downcasting safe in C++, if the derived class only have new methods(no new variables)?
struct Foo{
Foo(int val) : i(val){}
Foo &operator=(const Foo&){ //... }
void fun(){}
int i;
std::string s;
};
struct Bar : public Foo{
Bar(int i) : Foo(i){}
Bar &operator=(const Bar &other){
…
Theo Mars
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Why do we need to downcast a variable even if the function will upcast it again right before returning?
While reading a book about modern C++, I have seen a code snippet that confused me. The code has been written to set up PWM (16 bit Timer) for 8 bit AVR microcontroller. The code is like that:
class pwm_base : private util::noncopyable
{
…
BHOS
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2 answers
Interface downcasting with generics
I have the following code where I want to downcast to an interface with generic but I get Run-time exception: Unable to cast object of type 'FinalAssociator' to type 'IAssociator`1[Common]'.
public interface ICommon
{
string Name…
Ankan Kumar Giri
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Downcasting pointer to pointer
I'm learning polymorphism in C++ and I can't downcast a pointer to a pointer. I have a class Base and a class Derived that extends Base. And I want to do a pool of Derived objects using a function Base **derivedFactory(size_t size). I tried doing…
acampana
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Is there a way that i can make my object never null?
I was given a task and I'm not sure how to get it to work. All the test cases must pass.
Assertions.assertDoesNotThrow(() -> p3.equals(null));
Assertions.assertFalse(p3.equals(null), "equals to null should return false");
I figured out the first…
Zaid Fanek
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strange behavior of C++ downcasting on object
i ran the code below to assign parent portion of objet to child object.
but as described inline, c style downcast behaves something unexpected.
what happen there? please refer to the comment below.
struct A {
public:
int i{};
…
kile
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Java downcasting with two different subclasses
I am learning Java and have been playing with up and downcasting in my command prompt using the classes I defined in Eclipse. I am working with three classes that I included here, and my question is at the bottom:
public class Animal {
public…
Tech320
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Type parameters - get concrete type from type T : IMyInterface
Suppose I have a List...
I have three classes which implement IMyInterface: MyClass1, MyClass2, and MyClass3
I have a readonly Dictionary:
private static readonly Dictionary DeclarationTypes = new Dictionary
{
…
Conrad Clark
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Decoding a Codable with class type returned from a function actually returns an item with its superclass as type
I wrote a custom decoder for a json response where I have a "content" field that can be decoded to various different classes, all of them inheriting from the same ContentItem superclass. I also have a function that returns a class type, which I use…
Kappei
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Downcasting from superclass to several subclasses using Stream
That's my first post and it will be a tough one.
We have a list of Employee class elements, which at the same time can be elements of a 5 types of subclasses: ApprenticeEmployee, SalariedEmployee, CommissionEmployee, CommissionEmployeeWithSalary…
Ketterle
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