# Julia 1.10 introduces "Tuple field type cannot be Union{}" error in AlgebraOfGraphics.jl

**URL:** <https://discourse.julialang.org/t/julia-1-10-introduces-tuple-field-type-cannot-be-union-error-in-algebraofgraphics-jl/106389>\
**Category:** Internals & Design\
**Tags:** question\
**Created:** [November 17, 2023, 8:49pm UTC](https://discourse.julialang.org/t/julia-1-10-introduces-tuple-field-type-cannot-be-union-error-in-algebraofgraphics-jl/106389 "2023-11-17T20:49:39Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![rdboyes](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdboyes/32/204009_2.png) [@rdboyes](https://discourse.julialang.org/u/rdboyes)\
**Post date:** [November 17, 2023, 8:49pm UTC](https://discourse.julialang.org/t/julia-1-10-introduces-tuple-field-type-cannot-be-union-error-in-algebraofgraphics-jl/106389/1 "2023-11-17T20:49:39Z")

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Hi All -

I’m trying to fix an error introduced in AlgebraOfGraphics by Julia 1.10 and I’m having a hard time understanding what is actually happening. The error is now thrown any time the function AlgebraOfGraphics.density() is used, and I think it’s happening at one of the following lines:

```julia
_kde(data::NTuple{1, Any}; kwargs...) = kde(data...; kwargs...)
_kde(data::Tuple; kwargs...) = kde(data; kwargs...)

```

> <https://github.com/MakieOrg/AlgebraOfGraphics.jl/blob/c9753ff2cd094944642468af4208726f502fc982/src/transformations/density.jl#L9>

As a result of the following update to julia: [make Tuple{Union{}} unconstructable by vtjnash · Pull Request #49111 · JuliaLang/julia · GitHub](https://github.com/JuliaLang/julia/pull/49111)

But I’m just kind of lost as to 1. why this change was made and 2. what we’re supposed to do instead. Any help would be appreciated!

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**Author:** ![jameson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jameson/32/23_2.png) [@jameson](https://discourse.julialang.org/u/jameson)\
**Post date:** [November 17, 2023, 11:49pm UTC](https://discourse.julialang.org/t/julia-1-10-introduces-tuple-field-type-cannot-be-union-error-in-algebraofgraphics-jl/106389/2 "2023-11-17T23:49:51Z")

</div>

Can you post a full stack trace? I don’t see where this is trying to construct Tuple{Union{}} just from looking at it

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**Author:** ![rdboyes](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdboyes/32/204009_2.png) [@rdboyes](https://discourse.julialang.org/u/rdboyes)\
**Post date:** [November 18, 2023, 2:43pm UTC](https://discourse.julialang.org/t/julia-1-10-introduces-tuple-field-type-cannot-be-union-error-in-algebraofgraphics-jl/106389/3 "2023-11-18T14:43:08Z")

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Here’s a (modified) example from the AlgebraOfGraphics tutorial that will trigger the error:

```julia
using PalmerPenguins, DataFrames, AlgebraOfGraphics

penguins = dropmissing(DataFrame(PalmerPenguins.load()))

penguin_bill = data(penguins) * mapping(
    :bill_length_mm => (t -> t / 10) => "bill length (cm)",
    :bill_depth_mm => (t -> t / 10) => "bill depth (cm)",
)

plt = penguin_bill * density(npoints=50) * mapping(col = :species)

axis = (width = 225, height = 225)

draw(plt; axis = axis)

```

And the resulting stack trace:

```julia
ERROR: LoadError: Tuple field type cannot be Union{}
Stacktrace:
  [1] map(f::Function, d::Dictionaries.Indices{Union{}})
    @ Dictionaries C:\Users\Randy\.julia\packages\Dictionaries\7aBxp\src\map.jl:91
  [2] unnest(vs::Vector{@NamedTuple{}}, indices::Dictionaries.Indices{Union{}})
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\algebra\layer.jl:81
  [3] unnest_dictionaries(vs::Vector{@NamedTuple{}})
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\algebra\layer.jl:84
  [4] map(f::AlgebraOfGraphics.var"#192#193"{@NamedTuple{datalimits::Tuple{Tuple{Float64, Float64}, Tuple{Float64, Float64}}, npoints::Int64}}, processedlayer::ProcessedLayer)
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\algebra\layer.jl:101
  [5] (::AlgebraOfGraphics.DensityAnalysis{MakieCore.Automatic, MakieCore.Automatic, MakieCore.Automatic})(input::ProcessedLayer)
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\transformations\density.jl:30
  [6] process(layer::Layer)
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\algebra\processing.jl:102
  [7] iterate
    @ Base .\generator.jl:47 [inlined]
  [8] collect(itr::Base.Generator{Layers, typeof(AlgebraOfGraphics.process)})
    @ Base .\array.jl:832
  [9] map
    @ Base .\abstractarray.jl:3301 [inlined]
 [10] ProcessedLayers(a::Layer)
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\algebra\layers.jl:41
 [11] compute_axes_grid(d::Layer; axis::@NamedTuple{width::Int64, height::Int64}, palettes::@NamedTuple{})
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\algebra\layers.jl:114
 [12] compute_axes_grid
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\algebra\layers.jl:110 [inlined]
 [13] compute_axes_grid(fig::Makie.Figure, d::Layer; axis::@NamedTuple{width::Int64, height::Int64}, palettes::@NamedTuple{})
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\algebra\layers.jl:100
 [14] compute_axes_grid
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\algebra\layers.jl:97 [inlined]
 [15] #240
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\draw.jl:21 [inlined]
 [16] update
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\draw.jl:10 [inlined]
 [17] plot!(fig::Makie.Figure, d::Layer; axis::@NamedTuple{width::Int64, height::Int64}, palettes::@NamedTuple{})
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\draw.jl:21
 [18] plot!
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\draw.jl:16 [inlined]
 [19] (::AlgebraOfGraphics.var"#244#245"{@NamedTuple{width::Int64, height::Int64}, @NamedTuple{}, @NamedTuple{}, @NamedTuple{}, @NamedTuple{}, Layer})(f::Makie.Figure)
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\draw.jl:48
 [20] update
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\draw.jl:10 [inlined]
 [21] #draw#243
    @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\draw.jl:47 [inlined]
 [22] top-level scope
    @ c:\Users\Randy\.julia\dev\TidierPlots\scratch\density_test.jl:14
in expression starting at c:\Users\Randy\.julia\dev\TidierPlots\scratch\density_test.jl:14

```

---

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**Author:** ![jameson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jameson/32/23_2.png) [@jameson](https://discourse.julialang.org/u/jameson)\
**Post date:** [November 18, 2023, 5:46pm UTC](https://discourse.julialang.org/t/julia-1-10-introduces-tuple-field-type-cannot-be-union-error-in-algebraofgraphics-jl/106389/4 "2023-11-18T17:46:02Z")

</div>

Ah, I see. You should report this bug to Dictionaries then. It is using an unstable private API (Core.Compiler.return\_type) and appear to be not fully implementing the `Base.map` API correctly (the return type depends on inference. While, I think the usual implementations use `@default_eltype`?

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**Author:** ![Sukera](https://avatars.discourse-cdn.com/v4/letter/s/ce7236/32.png) [@Sukera](https://discourse.julialang.org/u/Sukera)\
**Post date:** [November 18, 2023, 6:31pm UTC](https://discourse.julialang.org/t/julia-1-10-introduces-tuple-field-type-cannot-be-union-error-in-algebraofgraphics-jl/106389/5 "2023-11-18T18:31:18Z")

</div>

> [@jameson](#):
>
> While, I think the usual implementations use `@default_eltype`?

That likely won’t help with getting away from internals:

```julia
help?> Base.@default_eltype
  │ Warning
  │
  │ The following bindings may be internal; they may change or be removed in future versions:
  │
  │ • Base.@default_eltype

  No documentation found for private symbol.

```

which in the end also uses `Core.Compiler.return_type`:

```julia
julia> @macroexpand Base.@default_eltype([19293])
quote
    #= array.jl:743 =#
    if [19293] isa Base.Generator && ([19293]).f isa Base.Type
        #= array.jl:744 =#
        var"#7#T" = ([19293]).f
    else
        #= array.jl:746 =#
        var"#7#T" = (Base.Core).Compiler.return_type(Base._iterator_upper_bound, Base.Tuple{Base.typeof([19293])})
    end
    #= array.jl:748 =#
    Base.promote_typejoin_union(var"#7#T")
end

```

I think for the case in Dictionaries.jl ([link](https://github.com/andyferris/Dictionaries.jl/blob/7b5b7b3aa80b9c3c4129a80d15dcd088682fb277/src/map.jl#L90-L94)) there isn’t really anything else to do other than rely on inference. The question is rather - what introduced that `Union{}` in the first place, seeing as its also present in the frames before Dictionaries.jl?

---

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**Author:** ![Sukera](https://avatars.discourse-cdn.com/v4/letter/s/ce7236/32.png) [@Sukera](https://discourse.julialang.org/u/Sukera)\
**Post date:** [November 18, 2023, 6:41pm UTC](https://discourse.julialang.org/t/julia-1-10-introduces-tuple-field-type-cannot-be-union-error-in-algebraofgraphics-jl/106389/6 "2023-11-18T18:41:07Z")

</div>

> [@rdboyes](#):
>
> ```julia
> [4] map(f::AlgebraOfGraphics.var"#192#193"{@NamedTuple{datalimits::Tuple{Tuple{Float64, Float64}, Tuple{Float64, Float64}}, npoints::Int64}}, processedlayer::ProcessedLayer)
> @ AlgebraOfGraphics C:\Users\Randy\.julia\packages\AlgebraOfGraphics\yhdjr\src\algebra\layer.jl:101
> 
> ```

Looking up the stackframes, I think it’s this that introduces the `Union{}` somehow:

> <https://github.com/MakieOrg/AlgebraOfGraphics.jl/blob/c9753ff2cd094944642468af4208726f502fc982/src/algebra/layer.jl#L96-L103>

I don’t know about the internals of AlgebraOfGraphics, but I think the question is why this causes `map(_ , outputs)` to be a `Vector{@NamedTuple{}}`.