Confusing error with mixed-type inputs

[aplavin]

I found a strange behaviour with mixed-type inputs. 2D arrays work correctly:

[(a=1,) (a='a',)] |> @filter(isa(_.a, Char)) |> collect

1-element Array{NamedTuple{(:a,),T} where T<:Tuple,1}:
 (a = 'a',)

However, 1D do not:

[(a=1,) (a='a',)][:] |> @filter(isa(_.a, Char)) |> collect

Schemaless sources cannot be passed to datavaluerows.

Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] datavaluerows(::Array{NamedTuple{(:a,),T} where T<:Tuple,1}) at /users/aplavin/.julia/packages/Tables/NEFJq/src/tofromdatavalues.jl:72
 [3] getiterator(::Array{NamedTuple{(:a,),T} where T<:Tuple,1}) at /users/aplavin/.julia/packages/Tables/NEFJq/src/Tables.jl:189
 [4] query(::Array{NamedTuple{(:a,),T} where T<:Tuple,1}) at /users/aplavin/.julia/packages/QueryOperators/PfROc/src/source_iterable.jl:7
 [5] (::getfield(Main, Symbol("##134#136")))(::Array{NamedTuple{(:a,),T} where T<:Tuple,1}) at /users/aplavin/.julia/packages/Query/UeHfO/src/standalone_query_macros.jl:221
 [6] |>(::Array{NamedTuple{(:a,),T} where T<:Tuple,1}, ::getfield(Main, Symbol("##134#136"))) at ./operators.jl:813
 [7] top-level scope at In[37]:1

[davidanthoff]

Hm, that is weird and it looks to me as if Tables.jl is doing some type piracy like thing here that it shouldn’t be doing. @quinnj, do you know why Tables.jl is inserting itself here at all?

[quinnj]

Tables.jl does define:

IteratorInterfaceExtensions.getiterator(x::RowTable) = datavaluerows(x)
IteratorInterfaceExtensions.isiterable(x::RowTable) = true

which is what is getting picked up here. These definitions on RowTable (which is just an alias for Vector{<:NamedTuple}) should be mostly invisible to users, but in this case, the Array type is Vector{NamedTuple{(:a,), T} where T <: Tuple}, which doesn't have a defined schema, but is still picked up for dispatch by this definition.

[davidanthoff]

Hm, that strikes me as not ideal, isn’t that just a case of type piracy that isn’t needed?

[quinnj]

We could probably just remove the getiterator definitions; not sure if that would break anything for people though.

[davidanthoff]

I think that would make sense. That is how it had worked for a long time before Tables.jl came onto the scene, so I'm not too worried that it would break anything to remove things.