Polymorphism in C++ when parsing user input - c++

Question

I am working on an application that parses user input (command) and tries to process the command. There are various types of command. So I created one Base class, which all commands will inherit from. Now I am trying to figure out how to correctly process the command. What I would like to do is to create an instance of the Base class and then somehow recast it to the correct descendant. Ideally, this would be done at the level of the command classes, eg Base, Der1, Der2, no in main function as in example.
main.cpp
#include "class1.hpp"
int main(int argc, const char * argv[]) {
Base com("some input");
com.process(); //based on the input I want to distinguish which of the derived classes should be used
}
class1.hpp
#include <iostream>
class Base {
std::string input;
public:
Base(std::string input) {
this->input = input;
}
virtual void process(){}
};
class Der1 {
public:
Der1(std::string input);
void process() {
std::cout << "Der1 process" << std::endl;
}
};
class Der2 {
public:
Der2(std::string input);
void process() {
std::cout << "Der2 process" << std::endl;
}
};
Is this correct attitude when parsing user input? Or maybe is there some different approach that I might try? I prefer to use polymorphism as part of learning c++.
Thank you for any answer.

Answer 1

Is this correct attitude when parsing user input?
In C++, we usually try to keep the full type instead of erasing it to a base class: then we need no virtual dispatch, can fully use templates/overloads etc.
Or maybe is there some different approach that I might try?
Definitely: try to use static polymorphism instead. I think in your example something like this would be enough:
struct Der1 {
Der1(std::string_view); // TODO
auto process() { return "processed by Der1"sv; }
};
struct Der2 {
Der2(std::string_view); // TODO
auto process() { return "processed by Der2"sv; }
};
auto process(std::string_view input) {
switch (input.at(0)) { // I don't know how you actually want to choose DerN
case '1': return Der1{input}.process();
case '2': return Der2{input}.process();
default: throw std::runtime_error{"couldn't decide how to process"};
}
}
int main() { std::cout << process("1some input") << '\n'; }