I know it’s a trivial proposal, but, should a primitive type data object belong to(∈, in) itself? Axiom of regularity implicates that “No set is an element of itself”.
Hmm, technically, 1 isn’t a set, so 1 isn’t an element of 1 it’s element of {1} though.
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The docs for in say
Determine whether an item is in the given collection, in the sense that it is == to one of the values generated by iterating over the collection.
In Julia, numbers are iterable:
julia> collect(1)
0-dimensional Array{Int64,0}:
1
and so 1 in 1 is true.
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Numbers being iterable collections containing themselves is a quirk (wart, depending on your POV) in Julia. See the lengthy discussions in
https://github.com/JuliaLang/julia/issues/11769
https://github.com/JuliaLang/julia/issues/7903
https://github.com/JuliaLang/julia/pull/19700
I understand why this was not addressed for 1.0, and now it would be breaking, but I hope this is revisited at some point for 2.0.
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