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.
Questions tagged [double-dispatch]
97 questions
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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 asValue() { return value ; }
I have tried this code…
kAmJi
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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
devtools, basic operations made possible with…
Brice Nocenti
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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.))
:a-collection
(foo "bar")
:a-string
This…
Daniel
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3 answers
Implementing double dispatch with two class hierarchies in C++
I want to create an event dispatch system with a (shallow) hierarchy of Events that can be observed by a (shallow) hierarchy of EventObservers. I figured double-dispatch would allow a wide variety of both Events and EventObservers without having to…
BrettW
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2 answers
std::shared_ptr and double callback
I have some logic where I am using std::shared_ptrs to objects in an inheritance hierarchy. At one point I need to handle these objects depending on their real type, so I am using a double dispatch (i.e. I call a method on the base class, which then…
LiKao
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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, LastPoint, etc., as well as some common properties.
I…
Nick Bull
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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 another class that performs type erasure at runtime.…
Adam
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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;
virtual void print(DocDoc *d)=0;
As I…
Mr.O
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How to Emulate Double Dispatch in Objective-C
I'm, trying to emulate a Double Dispatch in Objective-C.
I know Objective-C does not support function/method overloading. But can you emulate this?
Any idea.
Josué H.
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Can the below program be considered double dispatch example?
class Product
{
}
class Mobile extends Product
{
}
class Market
{
public void buy(Product product)
{
System.out.println("Search a product in market");
}
public void buy(Mobile mobile)
{
…
ahskid
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1 answer
Multiple dispatch and multi-methods
What are they, what's the different between them?
Many sources, like Wikipedia, claim they're the same thing, but others explicitly say the opposite, like sbi in this question:
First: "Visitor Pattern is a way to simulate Double Dispatching in…
peoro
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Mixing double dispatch and static polymorphism
I'm sure this is a bad idea. Let's pretend I have a good reason to do it. I have a tree of nodes that successfully uses static polymorphism to pass messages. Crucially, each node cannot the types of the nodes it connects to, it just knows the types…
Ian
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Is there a C++/CLI equivalent to a C# cast to a dynamic type?
I'm extending a class hierarchy written in C# that implements a Visitor pattern (double-dispatch) using the dynamic keyword, as described here.
Here is some very simplified pseudo-code of what I'm currently doing in C#:
public class Command {
…
BlueStrat
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Circular dependency with double dispatch
I'm trying to implement the double dispatch pattern but I get a circular dependency that I can't resolve with forward declaration (as it was resolved in this problem link).
Below is an example of my problem:
header 1:
class Object
{
virtual void…
dlavila
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3 answers
How can I implement double dispatch when I don't know all the classes in advance?
I've got a base class with (potentially) a lot of subclasses, and I would like to be able to compare any two objects of the base class for equality. I am trying to do this without invoking the blasphemous typeid keyword.
#include
struct…
Obliterax Scourge of Nations
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