Union and intersect with unexpected return types

Internals & Design
1

Tried the following:

  | | |_| | | | (_| |  |  Version 0.6.0 (2017-06-19 13:05 UTC)
 _/ |\__'_|_|_|\__'_|  |  
|__/                   |  x86_64-redhat-linux

julia> union(Set(Int16[1,2,3]), IntSet([1,42]))
4-element Array{Int64,1}:
  2
  3
  1
 42

julia> intersect(Set(Int16[1,2,3]), IntSet([1,42]))
1-element Array{Int64,1}:
 1

and was confused, why didn’t I see a Set, or IntSet but a Vector?
Interchanging the arguments helped, so that seemed not a design decision.

julia> intersect(IntSet([1,42]), Set(Int16[1,2,3]))
IntSet([1])

I found the bugs in base/set.jl:54 and :69

function union(s::Set, sets::Set...)

I think, the second Set should be AbstractSet there, otherwise the method falls back to

intersect(v1, vs...) in Base at array.jl:1854

which is responsible for the Array return type.

2

There does seem to be an issue here. I suggest you make a pull request with the suggested change and some tests.

3

Yes, I will do. But as I am rather novice, I need instructions how to set up a pull request. Unfortunately I could not find any hint in this forum and have to ask for a link.

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4

Start here, perhaps. It’s usually a good idea to get started and then ask for help when you get stuck, since then there’s some context and detail. Also, the Gitter/IRC and Slack channels have operators waiting for your call…

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5

Please do file an issue at least. If there’s already an issue, please link to it here so that one can follow the breadcrumbs.

6

This issue has bee fixed and merged into master:
https://github.com/JuliaLang/julia/pull/23139

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