Adds keys and values iterators

[mlodato517]

This PR
Adds keys and values iterator helpers to the MapReadRef per this comment.

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This change is 

[codecov]

Codecov Report

Merging #61 into master will increase coverage by 0.76%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #61      +/-   ##
==========================================
+ Coverage   82.78%   83.54%   +0.76%     
==========================================
  Files          12       12              
  Lines        1185     1234      +49     
==========================================
+ Hits          981     1031      +50     
+ Misses        204      203       -1     

Impacted Files	Coverage Δ
src/read/read_ref.rs	76.47% <100.00%> (+6.10%)	⬆️
tests/lib.rs	98.15% <100.00%> (+0.10%)	⬆️
tests/quick.rs	93.38% <100.00%> (+1.15%)	⬆️
src/write.rs	74.32% <0.00%> (-0.10%)	⬇️
src/read/mod.rs	78.40% <0.00%> (+1.39%)	⬆️

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[jonhoo]

This looks great once again, thank you!

[mlodato517]

You're welcome! And thanks for all your great reviews!

While writing these assertions I was thinking, "It might be convenient to implement Eq on Values if the inner value implements Eq". But I can't tell if it's just convenient for tests. Is that something you might want?

Otherwise, looking through the indexmap tests there are tests for map.values_mut(), map1 == map2, and then some stuff based on sort order that I'm guessing we don't care about because we don't care about order. Would you prefer that kind of functionality?

Above and beyond all that, are there any other things you've been looking to revisit/clean up that I could tackle? This comment looks like an obvious place to start. I could think on that if it's valuable. I'm not sure I'd be able to brain out something at this level, but I'd also be interested in trying 🤷

Or if there are any other projects you have or know about that need some more chores like this done (or easy features or whatever), I'm game!

[jonhoo]

It's been a pleasure!

I think PartialEq + Eq on Values is probably mostly useful for tests, but it seems reasonable enough to me! One thing that'll be tricky is to check that the cardinality is right if one thing is Short (but has duplicates) and the other thing is a Long.

I think the particular code comment you linked to is unlikely to matter much in practice, since it only every runs once for a given evmap. In general, a good strategy is to look for things that are missing in the coverage map and add tests for those. In terms of other issues, it would be awesome to add loom tests (#17), which will also require some thinking to get right.

As far as other projects go, here are a couple:

• griddle has some chore-like stuff in Implement missing APIs griddle#4 (RawEntry in particular)
• inferno has some test coverage bits in Improve test coverage for codebase inferno#63
• flurry needs more tests here Port and add more tests flurry#20