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From Cédric Champeau <cedric.champ...@gmail.com>
Subject Re: Towards a better compiler
Date Mon, 24 Apr 2017 08:56:36 GMT
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> Implementing equals/hashcode does not give you any order in a Set or Map
> you can rely on. Really, I still don´t get what you target with that. You
> require them in set to avoid duplicates.
>

I'm not talking about order here. I'm talking about reproducibility. A
linked hash set guarantees that things are read in the order they were
inserted. This is in general just enough. For example, we read in the
bytecode a list of interfaces, we add them to a set. If it's not linked,
then when we read them back, you have no guarantee. It has nothing to do
with _sorting_, which would reorder interfaces typically. The 2 uses cases
are different.

>
> then don´t. Let´s change the API to not return Set.


Yes. I would say +100 if it wasn't for performance. Typically if the
algorithm needs to use  `contains`, a `Set` is way more efficient. And
that's exactly why we use sets in lots of places. So to be clear, I did a
quick review of where we used sets and maps, and replaced that with linked
hash set and linked hash map when we needed both to guarantee that the
order of insertion is preserved (not an absolute order) *and* that the
algorithm required fast checks. This is all we need, I think. But I'm
calling for more than just a quick review, we should recheck all our usage
precisely. And avoid binary breaking changes, of course :)

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