Problems with parametric types

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I'm using Julia 1.5.2 on Win10

version 1: This one compiles. It actually works if all values of the Dict are of type 'V'. But that is not exactly what I want.

struct MyData{K,V} 
    data::AbstractVector{<:AbstractDict{<:K,V}}
end

version 2: This is what I actually want, but the compiler throws an UndefVarError: V not defined exception. The only different is {<:K,V} vs {<:K,<:V}

struct MyData{K,V} 
    data::AbstractVector{<:AbstractDict{<:K,<:V}}
end

Update: How to reproduce

julia> struct MyStruct{K,V}
           data::AbstractVector{<:AbstractDict{<:K,<:V}}
           end

julia> ar = [Dict{String,Any}("a" => 1)]
1-element Array{Dict{String,Any},1}:
 Dict("a" => 1)

julia> MyStruct(ar)
ERROR: UndefVarError: V not defined
Stacktrace:
 [1] MyStruct(::Array{Dict{String,Any},1}) at .\REPL[1]:2
 [2] top-level scope at REPL[3]:1

Any idea why that is and how to fix it?

thanks for your help

julia
1 Answers

This should be:

struct MyStructNew{K,V}
    data::AbstractVector{<:AbstractDict{K,V}}
end

That is is your parametric types need to be concrete:

Here is the test:

julia> MyStructNew(ar)
MyStructNew{String,Any}(Dict{String,Any}[Dict("a" => 1)])

julia> MyStructNew([Dict{Number, AbstractString}(3=>"a")])
MyStructNew{Number,AbstractString}(Dict{Number,AbstractString}[Dict(3 => "a")])

If you actually want the types of K and V to be abstract you can use your original struct but need to provide those types so Julia knows how to construct your object:

julia> struct MyStruct{K,V}
           data::AbstractVector{<:AbstractDict{<:K,<:V}}
       end

julia> MyStruct{AbstractString,Any}(ar)
MyStruct{AbstractString,Any}(Dict{String,Any}[Dict("a" => 1)])
user_99577100
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