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Confusing claim about HashMap in no_std #274

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justinmoon opened this issue Dec 2, 2020 · 4 comments
Open

Confusing claim about HashMap in no_std #274

justinmoon opened this issue Dec 2, 2020 · 4 comments

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@justinmoon
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This section claims the existence of a collections crate which can provide Vec and HashMap implementations.

I don't believe such a crate exists. Nothing comes up in crates.io. Vec is provided by alloc crate, but HashMap is not.

bors bot added a commit that referenced this issue Nov 8, 2022
333: Remove incorrect claim HashMap is avail in no_std r=adamgreig a=cameronelliott

This should fix and clear up #274, which has driven me crazy a few times.


Co-authored-by: Cameron Elliott <[email protected]>
@cameronelliott
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It is worth noting this page says the reason HM is not available is due to a lack of a secure random number generator:
https://stackoverflow.com/a/65470850/86375

@therealprof
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That statement is not quite right. There's no collections crate but a collections module in alloc (re-exported in std). The fact that HashMap (and HashSet) are only available in std rather than alloc due to an implicit requirement of a random generator is annoying but maybe it would be better to simply refer to hashbrown for now instead of highlighting an internal detail which is really no help for a user desperately longing for HashMap?

@cameronelliott
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@therealprof did you by chance look at the PR I submitted? Maybe you have some suggestions or improvement ideas for another PR? It actually sounds like a good idea to mention Hashbrown in that section of the docs.

@therealprof
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I did have a look. I would recommend making two more changes:

  • Change "collections crate" into e.g. "alloc::collections module"
  • Turn the "** HashMap and HashSet are not available due to a lack of a secure random number generator." remrk into a regular text, recommending to look into hashbrown if a HashMap or HashSet collection type is needed.

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