JavaScript is probably the most notable example of that. It used to not have a guaranteed iteration order, but browsers implemented it in such a way that the iteration order was the insertion order, and then that eventually got standardized because websites started depending on it.
For general purpose hash maps in standard libraries, I think you ought to either randomize the iteration order so that it's different every time, or guarantee an iteration order. Leaving it unspecified but predictable in practice is a recipe to fall victim to Hyrum's Law (https://www.hyrumslaw.com/).
For general purpose hash maps in standard libraries, I think you ought to either randomize the iteration order so that it's different every time, or guarantee an iteration order. Leaving it unspecified but predictable in practice is a recipe to fall victim to Hyrum's Law (https://www.hyrumslaw.com/).