ExampleBuilderStack

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

using namespace std::literals;

class Node {
    using Value = std::variant<nullptr_t, std::string, std::vector<Node>>;
    Value value_;

public:
    Node() = default;
    template <typename T>
    Node(T value)
        : value_(std::move(value))
    {
    }
    Value& GetValue() { return value_; }
};

int main()
{
    Node root;
    std::vector<Node*> stack_ { &root };
    // StartArray
    auto& curr_value = stack_.back()->GetValue();
    assert(std::holds_alternative<nullptr_t>(curr_value));
    curr_value = std::move(std::vector<Node> {});
    // Add value to array on stack
    auto& new_node = stack_.back()->GetValue();
    assert(std::holds_alternative<std::vector<Node>>(new_node));
    auto& node = std::get<std::vector<Node>>(new_node).emplace_back("simple_string");
    // the top of the stack is still an array
    auto new_back = stack_.back()->GetValue();
    assert(std::holds_alternative<std::vector<Node>>(new_back));
    // end array
    stack_.pop_back();
    auto& value = root.GetValue();
    assert(std::holds_alternative<std::vector<Node>>(value));
    std::cout << std::get<std::vector<Node>>(value).size() << '\n';
    auto simple_string = std::get<std::vector<Node>>(value).front();
    std::cout << std::get<std::string>(simple_string.GetValue());
}