Support for ordered insert/erase on json::object

[gummif]

I have a json that needs to be manipulated and maintaining the order of the keys in the object is really imported (even though it is supposed to be unordered key-value map).

Currently insertions are ordered so creating a json::object and inserting at the end will preserve the order. A work around I have now is something like this:

template<class K, class P>
void ordered_insert_before(boost::json::object& o, K&& key, P&& p)
{
	auto x = boost::json::object(o.storage());
	x.reserve(o.size() + 1);
	bool added = false;
	for (auto&& [k, v] : o)
	{
		if (k == key && !added)
		{
			x.insert(std::forward<P>(p));
			added = true;
		}
		x.insert(boost::json::object::value_type{std::move(k), std::move(v)});
	}
	if (!added)
	{
		x.insert(std::forward<P>(p));
	}
	o.swap(x);
}

template<class K>
void ordered_erase(boost::json::object& o, K&& key)
{
	auto x = boost::json::object(o.storage());
	x.reserve(o.size());
	for (auto&& [k, v] : o)
	{
		if (k != key)
		{
			x.insert(boost::json::object::value_type{std::move(k), std::move(v)});
		}
	}
	o.swap(x);
}

There are of course O(N). Is there interest for adding these as member functions or free functions with stronger ordering guarantees but worse O(N) complexity + allocations?

[vinniefalco]

In order to memmove the elements in the object correctly, the implementation would have to calculate the hash of each moved element, and adjust its index in the hash table.