`@set` with slices or broadcasting

[Jollywatt]

Hello, If I understand correctly, we may expect this to work out-of-the-box:

julia> using Accessors, StaticArrays

julia> s = SVector{4}(1:4) # immutable fixed size vector
4-element SVector{4, Int64} with indices SOneTo(4):
 1
 2
 3
 4

julia> @set s[2] += 100 # single indexing works
4-element SVector{4, Int64} with indices SOneTo(4):
   1
 102
   3
   4

julia> @set s[2:3] .+= 100 # broadcasted functions are not recognised
ERROR: UndefVarError: .+ not defined
Stacktrace:
 [1] top-level scope
   @ REPL[257]:1

julia> @set s[2:3] += [100, 100] # slicing fails ungracefully
ERROR: StackOverflowError:

Regarding the first error, the macro expands to something containing Accessors.:.+. We probably need to esc the operator symbol .+ so it gets evaluated to Base.Broadcast.BroadcastFunction(+), but I’m not sure if it’s that simple.

The second error seems like it needs more urgent attention. If s = [1, 2, 3] is a normal vector, @set s[2:3] += [100, 100] works fine, so it seems like this should be supported for static vectors.

[jw3126]

Thanks a lot for reporting! Broadcasting is tricky and not supported right now. Though I agree it would be nice to have. The

julia> @set s[2:3] += [100, 100] # slicing fails ungracefully
ERROR: StackOverflowError:

is a bug I would say. The ideal approach to fixing it would be to fix the following in StaticArrays.jl:

julia> Base.setindex(@SVector[1,2,3], [1,2], 1:2)
ERROR: StackOverflowError:
Stacktrace:
 [1] setindex(a::SVector{3, Int64}, x::Vector{Int64}, inds::UnitRange{Int64}) (repeats 79984 times)
   @ StaticArrays ~/.julia/packages/StaticArrays/6QFsp/src/deque.jl:198

and wait for this PR to land. If you want to get this fixed faster I am happy to guide you.

[aplavin]

and wait for this https://github.com/JuliaLang/julia/pull/46453 to land.

I don't think this is necessary. Just fixing StaticArrays setindex should be enough - it's just called in Accessors as is: https://github.com/JuliaObjects/Accessors.jl/blob/f0a65fe0edb542324574eaeef5680e78335415ba/src/staticarrays.jl#L3

[jw3126]

Ah thanks you are right @aplavin

[aplavin]

Broadcasting is now supported (Accessors#master, to be released soon)! All examples from the first post work on Vectors. The remaining SVector issues are because of their setindex method that leads to StackOverflow - yes, it is still the case. When that is fixed, Accessors will support it without any further changes. Would be useful if you opened an issue in the StaticArrays repo!

[Jollywatt]

You might have to be the one to open that StaticArrays issue, @aplavin — I've completely forgotten what this is all about!