Method do_render

src/include/minja/minja.hpp:975–1049

            : TemplateNode(loc), var_names(var_names), iterable(std::move(iterable)), condition(std::move(condition)), body(std::move(body)), recursive(recursive), else_body(std::move(else_body)) {}

    void do_render(std::ostringstream & out, const std::shared_ptr<Context> & context) const override {
      // https://jinja.palletsprojects.com/en/3.0.x/templates/#for
      if (!iterable) throw std::runtime_error("ForNode.iterable is null");
      if (!body) throw std::runtime_error("ForNode.body is null");

      auto iterable_value = iterable->evaluate(context);
      Value::CallableType loop_function;

      std::function<void(Value&)> visit = [&](Value& iter) {
          auto filtered_items = Value::array();
          if (!iter.is_null()) {
            if (!iterable_value.is_iterable()) {
              throw std::runtime_error("For loop iterable must be iterable: " + iterable_value.dump());
            }
            iterable_value.for_each([&](Value & item) {
                destructuring_assign(var_names, context, item);
                if (!condition || condition->evaluate(context).to_bool()) {
                  filtered_items.push_back(item);
                }
            });
          }
          if (filtered_items.empty()) {
            if (else_body) {
              else_body->render(out, context);
            }
          } else {
              auto loop = recursive ? Value::callable(loop_function) : Value::object();
              loop.set("length", (int64_t) filtered_items.size());

              size_t cycle_index = 0;
              loop.set("cycle", Value::callable([&](const std::shared_ptr<Context> &, ArgumentsValue & args) {
                  if (args.args.empty() || !args.kwargs.empty()) {
                      throw std::runtime_error("cycle() expects at least 1 positional argument and no named arg");
                  }
                  auto item = args.args[cycle_index];
                  cycle_index = (cycle_index + 1) % args.args.size();
                  return item;
              }));
              auto loop_context = Context::make(Value::object(), context);
              loop_context->set("loop", loop);
              for (size_t i = 0, n = filtered_items.size(); i < n; ++i) {
                  auto & item = filtered_items.at(i);
                  destructuring_assign(var_names, loop_context, item);
                  loop.set("index", (int64_t) i + 1);
                  loop.set("index0", (int64_t) i);
                  loop.set("revindex", (int64_t) (n - i));
                  loop.set("revindex0", (int64_t) (n - i - 1));
                  loop.set("length", (int64_t) n);
                  loop.set("first", i == 0);
                  loop.set("last", i == (n - 1));
                  loop.set("previtem", i > 0 ? filtered_items.at(i - 1) : Value());
                  loop.set("nextitem", i < n - 1 ? filtered_items.at(i + 1) : Value());
                  try {
                      body->render(out, loop_context);
                  } catch (const LoopControlException & e) {
                      if (e.control_type == LoopControlType::Break) break;
                      if (e.control_type == LoopControlType::Continue) continue;
                  }