ordered_json doesn't support range based erase

[jgannon65]

ordered_json uses ordered_map and ordered_map lacks a range based(iterator pair) erase method. This means that it's not possible to use algorithms like std::unique, std::remove_if etc on an ordered_json, even if you're trying to use it on a json array, bc it will not compile.

[nlohmann]

I can confirm this:

#include <iostream>
#include <nlohmann/json.hpp>
#include <algorithm>

using json = nlohmann::json;
using ordered_json = nlohmann::ordered_json;

int main() {
    json j = {1,2,2,4};
    //ordered_json j = {1,2,2,4}; // does not compile

    auto last = std::unique(j.begin(), j.end());
    j.erase(last, j.end());

    std::cout << j << std::endl;
}

This compiles with json, but not with ordered_json.

[nlohmann]

Feedback on #3109 greatly appreciated!

[nlohmann]

Help needed with #3109, see #3109 (comment).