map SOneTo to arrays? 🤷‍♀️

[fonsp]

This causes fonsp/Pluto.jl#458

MWE:

julia> using StaticArrays

julia> s = SA[1,2,3];

julia> i = eachindex(s)
SOneTo(3)

julia> map(i) do k
           []
       end
ERROR: setindex!() with non-isbitstype eltype is not supported by StaticArrays. Consider using SizedArray.
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] setindex! at /home/fons/.julia/packages/StaticArrays/LJQEe/src/MArray.jl:99 [inlined]
 [3] collect_to_with_first!(::MArray{Tuple{3},Array{Any,1},1,3}, ::Array{Any,1}, ::Base.Generator{SOneTo{3},var"#3#4"}, ::Int64) at ./array.jl:709
 [4] _collect(::SOneTo{3}, ::Base.Generator{SOneTo{3},var"#3#4"}, ::Base.EltypeUnknown, ::Base.HasShape{1}) at ./array.jl:704
 [5] collect_similar(::SOneTo{3}, ::Base.Generator{SOneTo{3},var"#3#4"}) at ./array.jl:628
 [6] map(::Function, ::SOneTo{3}) at ./abstractarray.jl:2162
 [7] top-level scope at REPL[6]:1

Note that this map is fine:

julia> map(i) do k
           2
       end
3-element MArray{Tuple{3},Int64,1,3} with indices SOneTo(3):
 2
 2
 2

Julia 1.5.2, StaticArrays v0.12.5

[c42f]

Would likely be fixed by #749

[andyferris]

The root cause here is that SOneTo is not a StaticArray (it subtypes AbstractUnitRange) and we don’t have most the methods defined for it and it is falling back to generic one from Base. Which is a problem in general and I’m not sure how much effort it would be to fix for all methods normally defined for static arrays...

[c42f]

The other more direct cause is that similar(SOneTo(3)) produces an MArray and setindex! isn't defined for MArray of non-isbits type. #749 would fix this, though I've been a little hesitant to merge that because it's inefficient.

But yes the underlying dispatch problem is that SOneTo <: AbstractUnitRange is not a subtype of StaticArray and can't really be made into one.