defining a custom getindex on a AbstractBasicDimArray is tricky

[tiemvanderdeure]

I am implementing the AbstractBasicDimArray interface on a bunch of objects in SDM.jl, and while lots of things work like a charm, getindex and siblings are really tricky to disambiguate.

The way I am doing this currently is that these objects have one field that is always a DimArray and does most of the work, and one or more fields with some extra info that shouldn't really be touched by something like getindex.

Maybe this is the price you pay for all the really great features of this package, but we could look into ways of making this less cumbersome. The low-hanging fruit would be to include an example in the docs (like for AbstractDimStack, if we end up making that a AbstractBasicDimArray), but maybe it's even possible to define a macro that does some of this work?

[rafaqz]

Yes it's complicated, it's hard enough handling ambiguity internally. But why do you need to add getindex methods, and which ones?

[tiemvanderdeure]

My idea here was to have an object that contains an array of MLJ machines but has SDM machines as an eltype, basically like so:

using DimensionalData
const DD = DimensionalData

struct MyEltype
    x
end

struct MyDimArray{N, D} <: DD.AbstractBasicDimArray{MyEltype, N, D}
    data::DimArray{<:Any, N, D}
end

DD.dims(d::MyDimArray) = DD.dims(d.data)

function Base.getindex(d::MyDimArray, I...; kw...)
    obj = Base.getindex(d.data, I...; kw...)
    if obj isa DD.AbstractDimArray
        MyDimArray(obj)
    else
        MyEltype(obj)
    end
end

Now this works great, except it generates a whole lot of method ambiguities. E.g.

myda = MyDimArray(rand(X(1:10), Y(1:10)))
myda[DimIndices(myda)]

ERROR: MethodError: getindex(::MyDimArray{2, Tuple{X{…}, Y{…}}}, ::DimIndices{Tuple{X{…}, Y{…}}, 2, Tuple{X{…}, Y{…}}}) is ambiguous.

Candidates:
  getindex(d::MyDimArray, I...; kw...)
    @ Main ~/juliadev/SpeciesDistributionModels/test/runtests.jl:105
  getindex(A::DimensionalData.AbstractBasicDimArray, i::DimIndices)
    @ DimensionalData ~/.julia/packages/DimensionalData/ejVFv/src/array/indexing.jl:102
  getindex(A::DimensionalData.AbstractBasicDimArray, d1::Union{Tuple{DimensionalData.Dimensions.Dimension, Vararg{DimensionalData.Dimensions.Dimension}}, AbstractArray{<:DimensionalData.Dimensions.Dimension}, AbstractArray{<:Tuple{DimensionalData.Dimensions.Dimension, Vararg{DimensionalData.Dimensions.Dimension}}}, DimIndices, DimSelectors, DimensionalData.Dimensions.Dimension}; kw...)
    @ DimensionalData ~/.julia/packages/DimensionalData/ejVFv/src/array/indexing.jl:83

Possible fix, define
  getindex(::MyDimArray{N, D} where {N, D<:Tuple}, ::DimIndices)

AFAIK I would have to work through all of those to get this working? Or am I just doing this all wrong?

[rafaqz]

function Base.getindex(d::MyDimArray, I::Int...)

This should be safe

[rafaqz]

function Base.getindex(d::MyDimArray, I:;Int...)

This should be safe, but also that looks like an AbstractDimArray not AbstractBasicDimArray. In which case just define parent and it will work