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Comment by yarg | Hacker News Reader

If you want insertion order you need something like a LinkedHashMap.

Java's had that forever, but it's not really a common use case.

I personally prefer something like Rust's `indexmap` instead, which is basically a hash table mapping from key to an index into a `Vec` containing the values. AFAIK this is also the approach taken by C#'s Dictionary.

I believe one rewrite of Python's dict was the first mainstream use of this sort of hash map as a default implementation.

I wish they provided a sort method to re-sort and re-index the vector to change the iteration order without the space overhead of creating a and sorting a separate vector/list of keys (or key-value pairs, depending on use case. You might want to change iteration order based on the currently held value).

> I believe one rewrite of Python's dict was the first mainstream use of this sort of hash map as a default implementation.

Technically pypy and I believe php implemented this model first, though it's probably most well known from cpython (for which it had been proposed first, by raymond hettinger).

I believe PHP is one of the (much) earlier languages with them.

Tcl was much earlier, in fact.

first time I know of LinkedHashMap is by reading a JSON library (Jason, iirc).

If you spend any amount of time programming Java, reviewing this list is a big help.

https://www.geeksforgeeks.org/collections-in-java-2/

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