# \[ANN\] 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:** 1\
**Showing post:** 23

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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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