Matt Godbolt sold me on Rust by showing me C++

  #include <exception>  
  #include <sstream>

  template <typename From, typename To>
  void convert_safely_helper_(From const& value, To& result) {
    std::stringstream sst;
    sst << value;
    sst >> result;
  }

  // Doesn't throw, just fails
  template <typename From, typename To>
  bool convert_safely(From const& value, To* result) {
    From check;
    convert_safely_helper_(value, *result);
    convert_safely_helper_(*result, check);
    if (check != value) {
      *result = To();
      return false;
    }
    return true;
  }

  // Throws on error
  template <typename To, typename From>
  To convert_safely(From const& value) {
    To result;
    if (!convert_safely(value, &result))
      throw std::logic_error("invalid conversion");
    return result;
  }

  #include <iostream>

  template <typename Buy, typename Quantity, typename Price>
  void sendOrder(const char* symbol, Buy buy, Quantity quantity, Price price) {
    std::cout << symbol << " " << convert_safely<bool>(buy) << " "
            << convert_safely<unsigned>(quantity) << " " << convert_safely<double>(price)
            << std::endl;
  }

  #define DISPLAY(expression)         \
    std::cout << #expression << ": "; \
    expression

  template <typename Function>
  void test(Function attempt) {
    try {
      attempt();
    } catch (const std::exception& error) {
      std::cout << "[Error: " << error.what() << "]" << std::endl;
    }
  }

  int main(void) {
    test([&] { DISPLAY(sendOrder("GOOG", true, 100, 1000.0)); });
    test([&] { DISPLAY(sendOrder("GOOG", true, 100.0, 1000)); });
    test([&] { DISPLAY(sendOrder("GOOG", true, -100, 1000)); });
    test([&] { DISPLAY(sendOrder("GOOG", true, 100.5, 1000)); });
    test([&] { DISPLAY(sendOrder("GOOG", 2, 100, 1000)); });
  }

  sendOrder("GOOG", true, 100, 1000.0): GOOG 1 100 1000
  sendOrder("GOOG", true, 100.0, 1000): GOOG 1 100 1000
  sendOrder("GOOG", true, -100, 1000): GOOG 1 [Error: invalid conversion]
  sendOrder("GOOG", true, 100.5, 1000): GOOG 1 [Error: invalid conversion]
  sendOrder("GOOG", 2, 100, 1000): GOOG [Error: invalid conversion]