Questions tagged [double-dispatch]
In software engineering, double dispatch is a special form of multiple dispatch and a mechanism that dispatches a function call to different concrete functions depending on the runtime types of two objects involved in the call. In most OO systems, the concrete function that is called from a function call in the code depends on the dynamic type of a single object and therefore they are known as single dispatch calls, or simply virtual function calls.
double-dispatch
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call non-virtual method of derived class in polymorphic hierarchy of library that can't be modified without down-casting
Today interviewer told me that Visitor pattern & double dispatch can be used to call non-virtual method of derived class from 3rd party library which source code can't be accessed/changed (this is ...
- 433
3
votes
1
answer
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views
Visitor Pattern and Double Dispatch
I know this is well trodden territory but I have a specific question... I promise.
Having spent very little time in the statically typed, object oriented world, I recently came across this design ...
- 2,762
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2
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How to get concrete type from mapping variable?
I have the following code:
const enum ShapeType {
Circle,
Rectangle
}
class Shape {
constructor(public shapeType: ShapeType) {}
}
class Circle extends Shape {
constructor(public x: number, ...
- 11.7k
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1
answer
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Double dispatch using visitor pattern in Java
I have this architecture:
In XMLFormulaFormatter, I need the value of instances of Constant (instances which are created in my Main class).
I have this method in the Constant class:
public double ...
- 97
0
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1
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362
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`vec_arith` double dispatch error with packages
I'm trying to implement the vctrs package, but specifically I'm trying to get the vec_arith double dispatch working.
The example code below works if I load this into the global environment, however it ...
- 2,061
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How to use a Double Dispatch with compareTo in JAVA?
A beginner of Java... I'm a bit confused by how to apply double dispatch (and visitor pattern) together with the compareTo method in JAVA.
Example Scenario:
Let's say I have an Animal interface where ...
- 164
1
vote
1
answer
236
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Wrong double dispatch method when putting a vctrs-built class in a package
I've created a new class to print percentages with vctrs, like explained in
https://vctrs.r-lib.org/articles/s3-vector.html .
It works well when I source the .R file. But when I build the package with
...
2
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0
answers
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Double dispatch in R: S4 vs vctrs library [closed]
If we want to implement a double dispatch method in R, we currently have two options to choose from:
S4 methods
vctrs library S3-based double dispatch
I especially mean arithmetic operators, such as ...
- 71
1
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1
answer
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How is an "isa?" based multimethod more than syntax sugar for instanceof?
I am taking an example from the clojure site.
(defmulti foo class)
(defmethod foo ::collection [c] :a-collection)
(defmethod foo String [s] :a-string)
(foo [])
:a-collection
(foo (java.util.HashMap....
- 556
2
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1
answer
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What exactly happened that we need double dispatch/visitor in c++
I understand the implementation of the solution and the double dispatch/visitor pattern, however I don't understand what happens at compile time and run-time that we need this pattern.
For example ...
- 254
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Forward declaring class with templated code
I'm trying to implement the double dispatch pattern for a message interface in C++. However, I find that I have to be too verbose in my handler class due to having to forward declare each message.
I'...
- 27
1
vote
1
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97
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Overloading method without modifying classes
I have access to a class structure, which I cannot modify, as follows:
Graphics
Circle
Line
etc.
Again, I cannot modify it! These all have individual properties such as Radius, FirstPoint, ...
- 9,696
0
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1
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97
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Passing shared_ptr<Base> as shared_ptr<Derived>
I currently have the following structure
class A
class B : public A
class C : public A
I have virtual methods defined in A and B and C are overriding them. The methods are of the sort
bool C::...
- 313
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C++ Double dispatch with runtime polymorphism?
Is it possible to perform double dispatch with runtime polymorphism?
Say I have some classes, and some of those classes can be added/multiplied/etc., and I want to store those dynamically within ...
- 313
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C++ double dispatch example
I got this code as an example of use of double dispatch, but I don't really understand one part of the code. creating the "abstract class" Printer, why I need to add:
virtual void print(PDFDoc *d)=0;
...
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