SimpleBuilder

#include <iostream>
#include <string>
#include <variant>
#include <vector>

struct Node;
using Value=std::variant<std::nullptr_t,int, std::string, std::vector<Node>>;
struct Node {
    Value value{};
};

std::ostream& operator<<(std::ostream& out, Value const& v) {
    if (std::holds_alternative<int>(v)) {
        out << std::get<int>(v);
    } else {
        out << "some text";
    }
    return out;
}

auto main() -> int {
    Node root;
    std::vector<Node*> stack{&root};
    int val = 42;
    auto& GetVal = stack.back();
    if (!std::holds_alternative<std::nullptr_t>(GetVal->value)) {
        throw std::logic_error("oi - vei! vse propalo!!");
    }
    GetVal->value = val;
    stack.pop_back();
    std::cout << root.value;
}