# \[ANN\] Dictionaries.jl - Improved productivity and performance of dictionaries in Julia

**URL:** <https://discourse.julialang.org/t/ann-dictionaries-jl-improved-productivity-and-performance-of-dictionaries-in-julia/32074>\
**Category:** Package Announcements\
**Tags:** dictionary, dictionaries\
**Created:** [December 9, 2019, 10:42pm UTC](https://discourse.julialang.org/t/ann-dictionaries-jl-improved-productivity-and-performance-of-dictionaries-in-julia/32074 "2019-12-09T22:42:50Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![Zach\_Christensen](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/zach_christensen/32/7220_2.png) [@Zach\_Christensen](https://discourse.julialang.org/u/Zach_Christensen)\
**Post date:** [December 12, 2019, 11:23am UTC](https://discourse.julialang.org/t/ann-dictionaries-jl-improved-productivity-and-performance-of-dictionaries-in-julia/32074/21 "2019-12-12T11:23:14Z")

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I’ve tried to limit the package to stuff that I feel could conceivably put in base someday. I’m sure someone smarter than me will take some of it and make a far better version before that ever happens though.

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**Author:** ![andyferris](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andyferris/32/235_2.png) [@andyferris](https://discourse.julialang.org/u/andyferris)\
**Post date:** [December 14, 2019, 10:52am UTC](https://discourse.julialang.org/t/ann-dictionaries-jl-improved-productivity-and-performance-of-dictionaries-in-julia/32074/22 "2019-12-14T10:52:14Z")

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> [@tkf](#):
>
> Does it mean there would be (say) `MutableIndices` and `FrozenIndices` types?

Yes I suppose we would statically encode the “insertability” of the indices at the type level, somehow. At the abstract level I’d rather use traits over abstract subtypes of `AbstractIndices`, though.

> I thought you can just go ahead and define custom mutable and immutable indices types for now and then swap its internal based on `Base.freeze` / `Base.melt` , once #31630 is merged. (And also maybe add `unsafe_freeze` API to do “manual borrow checker” to avoid copying until #31630 arrives?) This, of course, relies on that the design of #31630 does not deviate much from the current version. But do you see pitfalls other than that?

Yeah, I’m already prototyping so much that I was afraid of getting too far ahead would start to make things over-ambitious, but yes we can do that. Ideally we’d overload functions that are defined prior to _Dictionaries.jl_ though (really… we’ve needed to expand our traits for arrays and containers in general for a while now, so some shared package where we deal with these “container” ideas may be ideal).

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**Author:** ![tkf](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tkf/32/17635_2.png) [@tkf](https://discourse.julialang.org/u/tkf)\
**Post date:** [December 15, 2019, 3:30am UTC](https://discourse.julialang.org/t/ann-dictionaries-jl-improved-productivity-and-performance-of-dictionaries-in-julia/32074/23 "2019-12-15T03:30:11Z")

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Yeah, it would be nice to factor out mutability traits/implementations as a different package, so that Dictionaries.jl does not have to be responsible for all the advanced prototypings. IIUC DataFrames.jl also need something similar for `names(df)` and `df[!, col]`. But, [previous discussion](https://discourse.julialang.org/t/convention-for-read-only-array-getters/19356) (and the resulting package [ReadOnlyArrays.jl](https://github.com/bkamins/ReadOnlyArrays.jl)) did not explore mutability of indices/shape, IIRC. [ArrayInterface.jl](https://github.com/JuliaDiffEq/ArrayInterface.jl) has similar traits (e.g., `ismutable`) but it focuses on the mutability of values and not indices. Also, it focuses on arrays and not containers in general. Anyway, I guess you are already aware of many of these. I’m just re-emphasising that there are immediate needs for this in Julia ecosystem.

Looking at DataFrames, it looks like it still is not using ReadOnlyArrays. I wonder if there is still a plan to use this. As it needs two kinds of immutabilities (immutable values and immutable indices/shape), it looks like the best place for this to happen.

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