Downcasting permits an object of a superclass type to be treated as an object of any subclass type.
Questions tagged [downcast]
589 questions
5
votes
1 answer
Why can't I downcast pointer to members in template arguments?
If I make a pointer-to-base-member, I can convert it to a pointer-to-derived-member usually, but not when used within a template like Buzz below, where the first template argument influences the second one. Am I fighting compiler bugs or does the…
Joseph Garvin
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votes
3 answers
How do I down-cast a c++ object from a python SWIG wrapper?
The problem: I've wrapped some c++ code in python using SWIG. On the python side, I want to take a wrapped c++ pointer and down-cast it to be a pointer to a subclass. I've added a new c++ function to the SWIG .i file that does this down-casting, but…
SuperElectric
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Does c++ guarantee down-casting grandmother base class to grand child class like curiously recurring template pattern?
I would like to know whether c++ guarantees down-casting grandmother base class to grand child class like curiously recurring template pattern.
The following code works well in my environment. However I am not sure it works any…
mora
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dynamic_cast "this" to derived type: when is it legal?
Here is a code that obviously doesn't work, since downcasting "this" in a constructor is illegal:
#include
class A {
protected:
virtual ~A() {}
public:
A();
};
class B : public A {
};
A::A() {
…
sunmat
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How to downcast from non-polymorphic virtual base class?
Is there a way to downcast from a virtual base class to a derived class when there are no virtual functions involved? Here's some code to demonstrate what I'm talking about:
struct Base1
{
int data;
};
struct Base2
{
char…
Angew is no longer proud of SO
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How to force downcast on generics
Given the code below:
class Animal
{ }
class Dog : Animal
{ }
class Cage
{
private T animal;
public Cage(T animal)
{
this.animal = animal;
}
public T Animal
{
get { return animal;}
}
}
class…
user1778378
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4
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2 answers
Is it safe to downcast objects (not pointers) to their known derived type?
Would there be a danger of slicing
result Compare(const Osp::Base::Object &obj1, const Osp::Base::Object &obj2, int &cmp) const {
cmp = ((const Block)obj1).NumSuperBlocks() - ((const Block)obj2).NumSuperBlocks();
}
Where
class Block : Object…
John
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4
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1 answer
Lifetime error while attempting to downcast
I have a linked list of errors which I'm trying to traverse.
Given MyError, which is a linked list of errors with an optional code, my goal is to traverse the chain and return the first non-None code:
type BoxedError = Box
Shmoopy
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How to downcast integer multiindex level?
I have a dictionary of large scale MultiIndex series where both index levels are datetime values.
The abstract short example of one of it is:
idx_level_0 = pd.date_range('2020-01-01', '2020-04-01', freq = 'M')
idx_level_1 =…
igharok
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4
votes
1 answer
In C++, is it possible to use CRTP with a private base?
In C++ I have many classes, unrelated by inheritance, that define a method std::string get_name() const.
There are several utility functions that many classes need that are implemented in terms of get_name(). I would like classes that implement…
user1806566
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How to avoid downcasting when trying to extend a Java object
I get several objects of type Foo from a call to an external API. Locally I want to process those objects with a little added information so I have a subclass FooSon that adds those extra fields. How can I convert all those objects I get, to my new…
Omar Kohl
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dynamic_cast in C++ doesn't work without having RTTI on; Why?
Virtual methods work without RTTI, shouldn't that mean there's enough data around at runtime to figure out which class it is?
(i want to find out how i can downcast and then check if it was a pointer to the right type. i can't modify the classes…
Matthias
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How to access class specific methods without instanceof or getClass
Suppose I have the following interface and implementation:
interface Weapon{
int attack();
}
public class Sword implements Weapon {
//Constructor, and Weapon interface implementation
//...
public void…
user8753793
4
votes
3 answers
Polymorphism and downcasting questions
I'm reading up a book on Java and currently on the Polymorphism topic as well as how to downcast a reference variable. However, I'm pretty stuck with understanding the concept of downcasting. Below is the uml for the example I'm following.
For all…
Scorpiorian83
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Downcasting a generic type in C# 3.5
Why can I only upcast a generic and not downcast it?
How is it not clear to the compiler that if my constraint says where T : BaseClass and U is derived from BaseClass that (U)objectOfTypeT is valid?
the_drow
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