الگوی بازدیدگر

#include <iostream>
#include <vector>

class AbstractDispatcher; // Forward declare AbstractDispatcher

class File { // Parent class for the elements (ArchivedFile, SplitFile and ExtractedFile)
public:
// This function accepts an object of any class derived from AbstractDispatcher and must be implemented in all derived classes
virtual void accept(AbstractDispatcher &dispatcher) = 0;
};

// Forward declare specific elements (files) to be dispatched
class ArchivedFile;
class SplitFile;
class ExtractedFile;

class AbstractDispatcher { // Declares the interface for the dispatcher
public:
// Declare overloads for each kind of a file to dispatch
virtual void dispatch(ArchivedFile &file) = 0;
virtual void dispatch(SplitFile &file) = 0;
virtual void dispatch(ExtractedFile &file) = 0;
};

class ArchivedFile: public File { // Specific element class #1
public:
// Resolved at runtime, it calls the dispatcher's overloaded function, corresponding to ArchivedFile.
void accept(AbstractDispatcher &dispatcher) override {
dispatcher.dispatch(*this);
}
};

class SplitFile: public File { // Specific element class #2
public:
// Resolved at runtime, it calls the dispatcher's overloaded function, corresponding to SplitFile.
void accept(AbstractDispatcher &dispatcher) override {
dispatcher.dispatch(*this);
}
};

class ExtractedFile: public File { // Specific element class #3
public:
// Resolved at runtime, it calls the dispatcher's overloaded function, corresponding to ExtractedFile.
void accept(AbstractDispatcher &dispatcher) override {
dispatcher.dispatch(*this);
}
};

class Dispatcher: public AbstractDispatcher { // Implements dispatching of all kind of elements (files)
public:
void dispatch(ArchivedFile &) override {
std::cout <<"dispatching ArchivedFile" <<std::endl;
}

void dispatch(SplitFile &) override {
std::cout <<"dispatching SplitFile" <<std::endl;
}

void dispatch(ExtractedFile &) override {
std::cout <<"dispatching ExtractedFile" <<std::endl;
}
};

int main() {
ArchivedFile archivedFile;
SplitFile splitFile;
ExtractedFile extractedFile;

std::vector<File*> files;
files.push_back(&archivedFile);
files.push_back(&splitFile);
files.push_back(&extractedFile);

Dispatcher dispatcher;

for (File* file : files) {
file->accept(dispatcher);
}
}