why add assert in const_reference operator[](const typename object_t::key_type& key) const instead of just throw a exception

[h20282]

I noticed there is a difference between adding or not adding 'const' when using json::operator []

#include <iostream>

#include "nlohmann/json.hpp"

int main() {
    nlohmann::json json{{"b", "1"}}; // without const
    try {
        int a = json["a"]; // crash
        std::cout << "a = " << a << std::endl;
    } catch (const nlohmann::json::exception &e) {
        std::cout << e.what() << std::endl;
    }

    std::cout <<"end";
}

#include <iostream>

#include "nlohmann/json.hpp"

int main() {
    const nlohmann::json json{{"b", "1"}}; // with const
    try {
        int a = json["a"];
        std::cout << "a = " << a << std::endl;
    } catch (const nlohmann::json::exception &e) {
        std::cout << e.what() << std::endl; // exception catched
    }

    std::cout <<"end";
}

To figure out why they are different, I got this code:

https://github.com/nlohmann/json/blob/develop/include/nlohmann/json.hpp#L2147

so, why not just throw a exception?

[nlohmann]

See https://json.nlohmann.me/features/element_access/unchecked_access/#overview

Basically, operator[] offers unchecked access. Use at if you prefer exceptions instead of undefined behavior.