Double Dispatch in C++ is a mechanism that dispatches a function call to different concrete functions depending on the runtime types of two objects involved in the call. In more simple words, its function calling using two different virtual tables of respective two objects. I know this sounds cryptic, but don't worry I will come to double dispatch solution after trying most of the naive solution so that you will come away with the full understanding of concept without having needless confusions.
Motivation
- At first, a pointer to a base class made sense; you didn't need to know the actual derived class. So you decided to expose a single collection of base class pointers to your clients like so:
C++
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struct Animal {
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virtual const char *name() = 0;
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};
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using AnimalList = vector<Animal*>;
Behavioral Design Patterns: Visitor
Our last pattern of the behavioral design patterns is going to be the visitor pattern.
We use the visitor pattern when we want to make it possible to define a new operation for classes of an object structure without changing the classes.