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<h1 id="design-command-pattern"><a class="header" href="#design-command-pattern">design command pattern</a></h1>
<pre><code class="language-c++">
#include <iostream>
#include <memory>
#include <vector>
#include <stack>
#include <functional>
#include <unordered_map>
#include <string>
#include <stdexcept>
#include <chrono>
#include <thread>
// Command Interface
class Command {
public:
virtual void execute() = 0;
virtual void undo() = 0;
virtual ~Command() = default;
};
// Receiver Class (Object that performs the actual work)
class TextEditor {
public:
void insertText(const std::string& text) {
content += text;
std::cout << "Inserted: " << text << std::endl;
}
void deleteText(size_t count) {
if (count > content.length()) {
count = content.length();
}
deletedText = content.substr(content.length() - count);
content = content.substr(0, content.length() - count);
std::cout << "Deleted: " << deletedText << std::endl;
}
std::string getContent() const {
return content;
}
private:
std::string content;
std::string deletedText;
};
// Concrete Command for Text Insertion
class InsertTextCommand : public Command {
public:
InsertTextCommand(TextEditor& editor, const std::string& text)
: editor(editor), text(text) {}
void execute() override {
editor.insertText(text);
}
void undo() override {
editor.deleteText(text.length());
}
private:
TextEditor& editor;
std::string text;
};
// Concrete Command for Text Deletion
class DeleteTextCommand : public Command {
public:
DeleteTextCommand(TextEditor& editor, size_t count)
: editor(editor), count(count) {}
void execute() override {
editor.deleteText(count);
}
void undo() override {
// We would need to store the deleted text in the actual implementation
// This is a simplified version
throw std::runtime_error("Undo not fully implemented");
}
private:
TextEditor& editor;
size_t count;
};
// Command Invoker (Manages command execution and history)
class CommandInvoker {
public:
void executeCommand(std::unique_ptr<Command> command) {
command->execute();
commandHistory.push(std::move(command));
}
void undo() {
if (!commandHistory.empty()) {
auto command = std::move(commandHistory.top());
commandHistory.pop();
command->undo();
}
}
private:
std::stack<std::unique_ptr<Command>> commandHistory;
};
// Macro Command (Composite Command)
class MacroCommand : public Command {
public:
void addCommand(std::unique_ptr<Command> command) {
commands.push_back(std::move(command));
}
void execute() override {
for (auto& command : commands) {
command->execute();
}
}
void undo() override {
// Undo in reverse order
for (auto it = commands.rbegin(); it != commands.rend(); ++it) {
(*it)->undo();
}
}
private:
std::vector<std::unique_ptr<Command>> commands;
};
// Command Factory
class CommandFactory {
public:
using CommandCreator = std::function<std::unique_ptr<Command>()>;
void registerCommand(const std::string& name, CommandCreator creator) {
commandRegistry[name] = creator;
}
std::unique_ptr<Command> createCommand(const std::string& name) {
auto it = commandRegistry.find(name);
if (it != commandRegistry.end()) {
return it->second();
}
throw std::runtime_error("Unknown command");
}
private:
std::unordered_map<std::string, CommandCreator> commandRegistry;
};
// Functional Command (Modern C++ Approach)
class FunctionalCommand {
public:
template<typename Func>
class Command {
public:
Command(Func executeFunc, Func undoFunc)
: execute(executeFunc), undo(undoFunc) {}
void operator()() { execute(); }
void rollback() { undo(); }
private:
Func execute;
Func undo;
};
template<typename Func>
static auto create(Func executeFunc, Func undoFunc) {
return Command<Func>(executeFunc, undoFunc);
}
};
// Thread-Safe Command Executor
class ThreadSafeCommandExecutor {
public:
void enqueueCommand(std::unique_ptr<Command> command) {
std::lock_guard<std::mutex> lock(mutex);
commandQueue.push(std::move(command));
}
void processCommands() {
while (true) {
std::unique_ptr<Command> command;
{
std::lock_guard<std::mutex> lock(mutex);
if (commandQueue.empty()) {
break;
}
command = std::move(commandQueue.front());
commandQueue.pop();
}
command->execute();
// Simulate processing time
std::this_thread::sleep_for(std::chrono::milliseconds(100));
}
}
private:
std::queue<std::unique_ptr<Command>> commandQueue;
std::mutex mutex;
};
int main() {
// Basic Command Pattern Demonstration
{
TextEditor editor;
CommandInvoker invoker;
// Execute commands
invoker.executeCommand(
std::make_unique<InsertTextCommand>(editor, "Hello ")
);
invoker.executeCommand(
std::make_unique<InsertTextCommand>(editor, "World!")
);
std::cout << "Current Content: " << editor.getContent() << std::endl;
// Undo last command
invoker.undo();
std::cout << "After Undo: " << editor.getContent() << std::endl;
}
// Macro Command Demonstration
{
TextEditor editor;
MacroCommand macroCommand;
macroCommand.addCommand(
std::make_unique<InsertTextCommand>(editor, "Hello ")
);
macroCommand.addCommand(
std::make_unique<InsertTextCommand>(editor, "World!")
);
macroCommand.execute();
std::cout << "Macro Command Content: " << editor.getContent() << std::endl;
}
// Command Factory Demonstration
{
TextEditor editor;
CommandFactory factory;
// Register commands
factory.registerCommand("insert", [&]() {
return std::make_unique<InsertTextCommand>(editor, "Hello ");
});
// Create and execute command
auto command = factory.createCommand("insert");
command->execute();
}
// Functional Command Demonstration
{
int value = 0;
auto incrementCmd = FunctionalCommand::create(
[&]() { value++; },
[&]() { value--; }
);
incrementCmd();
std::cout << "Value after increment: " << value << std::endl;
}
return 0;
}
</code></pre>
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