# Julia set data structure
**URL:** https://discourse.julialang.org/t/julia-set-data-structure/1292
**Category:** Offtopic
**Created:** [January 4, 2017, 9:39pm UTC](https://discourse.julialang.org/t/julia-set-data-structure/1292 "2017-01-04T21:39:13Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@harven](https://discourse.julialang.org/u/harven)
#### Post date: [January 4, 2017, 9:39pm UTC](https://discourse.julialang.org/t/julia-set-data-structure/1292/1 "2017-01-04T21:39:13Z")
I have a question on the `set` data structure in base Julia. As far as I understand, it is mutable, with O(1) membership, and adding an element is done with `push!`, which modifies the set.
Is there a “functional” set collection that is immutable and for which “adding” elements proceeds by sharing? Or a simple way to emulate this behavior with the default set structure? At the moment, I am using
```
(s,x) -> union(s, Set(x))
```
in order to get a new set with `x` added without modifying `s` but it is probably not very efficient.
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### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [January 4, 2017, 10:07pm UTC](https://discourse.julialang.org/t/julia-set-data-structure/1292/2 "2017-01-04T22:07:41Z")
[https://github.com/JuliaLang/FunctionalCollections.jl](https://github.com/JuliaLang/FunctionalCollections.jl) ?
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### Author:  [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)
#### Post date: [January 4, 2017, 11:46pm UTC](https://discourse.julialang.org/t/julia-set-data-structure/1292/3 "2017-01-04T23:46:53Z")
That was written a while ago and has had very light maintenance, but it may work.
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### Author:  [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)
#### Post date: [January 5, 2017, 2:11am UTC](https://discourse.julialang.org/t/julia-set-data-structure/1292/4 "2017-01-05T02:11:59Z")
Well, it’s code is very simple. The tests fail, but it probably just needs some PRs to update from deprecated syntax. Sounds like a very good contribution opportunity for a newcomer.
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### Author:  [@felix](https://discourse.julialang.org/u/felix)
#### Post date: [January 9, 2017, 5:02pm UTC](https://discourse.julialang.org/t/julia-set-data-structure/1292/5 "2017-01-09T17:02:44Z")
Chris, I was glad to see such an opportunity pointed out. Thanks!
I gave it a go here [RFC: syntax update by felixrehren · Pull Request #29 · JuliaCollections/FunctionalCollections.jl · GitHub](https://github.com/JuliaLang/FunctionalCollections.jl/pull/29) and would appreciate any help in improving the PR until it is useful 🙂