join does not work for subobjects using ACSetTransformation

[slwu89]

Based on the zulip discussion, on Catlab v0.16.17. Using join on a vector of subobjects does not work. Interestingly as well, join(subobjs) and join(subobjs, SubOpBoolean()) for some reason still dispatch to the Base.join that turns them into a string. Only join(subobjs, SubOpWithLimits()) dispatches correctly to the method defined in Catlab. The naive method of union-ing together the components of the subobjects of interest works.

using Catlab, StatsBase

@present SchMyGraph <: SchGraph begin
    (EAttr,VAttr)::AttrType
    vattr::Attr(V,VAttr)
    eattr::Attr(E,EAttr)
end

@acset_type MyGraph(SchMyGraph, index=[:src,:tgt]) <: AbstractGraph

mygraph = erdos_renyi(MyGraph{Float64,String}, 70, 0.15)

# to_graphviz(mygraph, prog="fdp")

mygraph[:, :vattr] = "v" .* string.(parts(mygraph, :V))
mygraph[:, :eattr] = rand(nparts(mygraph, :E))

# make many subobjects
subobjs = [
    let 
        v1, v2 = sample(parts(mygraph, :V), 2, replace=false)
        edg = edges(mygraph, v1, v2)
        Subobject(mygraph, (V=[v1,v2], E=collect(edg)))
    end
    for _ in 1:20
]

# do not work
join(subobjs)
join(subobjs, SubOpWithLimits())
join(subobjs, SubOpBoolean())

# works
glued_subobj = Subobject(
    mygraph,
    (
        V=unique(vcat(collect.(getindex.(components.(subobjs), :V))...)),
        E=unique(vcat(collect.(getindex.(components.(subobjs), :E))...))
    )
)

dom(hom(glued_subobj))

# to_graphviz(glued_subobj, prog="fdp")