Thanks, I managed to figure it out by re-re-re-reading the docs. I was
suspecting that the answer will be about parametric types.
function df_to_m{T<:Jinnie.Jinnie_Model}(df::DataFrames.DataFrame, m::T) #
works!
Is this the only way? I'm fine with it (it's very explicit upon reading)
but it's unexpected coming from OOP where you get polymorphism out of the
box (subtypes can be used instead of the parent type, without needing
anything else).
sâmbătă, 27 februarie 2016, 09:31:23 UTC+1, Adrian Salceanu a scris:
>
> Hi,
>
> I stumbled upon an issue in my code and I can't quite figure out the
> behavior. Any hints would be much appreciated, thanks in advance.
>
> So, I have a function:
>
> function df_to_m(df::DataFrames.DataFrame, m::Jinnie_Model)
>
> It iterates over each row of the df DataFrame and instantiates the
> corresponding m model type, returning an array of m model instances.
>
> For example, say if I have this DataFrame (*df*)
>
> 1x3 DataFrames.DataFrame
> | Row | name | url | updated_at
> |
>
> |-----|---------|---------------------------------------|------------------------------|
> | 1 | "Bokeh" | "git://github.com/bokeh/Bokeh.jl.git" | "2016-02-10
> 19:21:57.209996" |
>
> I would call
>
> df_to_m(df, Jinnie.Package())
>
> and expect to get
>
> 1-element Array{Any,1}:
> Jinnie.Package("packages","name","Bokeh","git://
> github.com/bokeh/Bokeh.jl.git")
>
> where Jinnie_Model is an abstract type defined in the Jinnie module as
>
> abstract Jinnie_Model
>
> and Jinnie.Package extends Jinnie_Model
>
> type Package <: Jinnie_Model
> _table_name::AbstractString
> _id::AbstractString
> name::AbstractString
> url::AbstractString
>
> Package(; name = "", url = "") = new("packages", "name", name, url)
> end
>
> However, the problem is that df_to_m does not want to accept subtypes of
> Jinnie_Model:
>
> ERROR: MethodError: `df_to_m` has no method matching
> df_to_m(::DataFrames.DataFrame, ::Jinnie.Package)
> Closest candidates are:
> df_to_m(::DataFrames.DataFrame, ::Jinnie.Jinnie_Model)
>
> If I drop the type constraint in the function's definition, it works
> great, as expected:
>
> function df_to_m(df::DataFrames.DataFrame, m) # this version works
>
> ==================================
>
> My questions are:
>
> 1. how can I get the function to accept subtypes of Jinnie_Model while
> keeping the type constraint?
>
> 2. I don't like passing instances like Jinnie.Package() and I would
> rather pass the type itself Jinnie.Package into the polymorphic function.
> It's a crappy code smell so I must be doing something wrong.
>
> I experimented with defining the function as
>
> function df_to_m(df::DataFrames.DataFrame, m::Type{Jinnie.Jinnie_Model})
>
> but got the same error, polymorphism be damned.
>
> ERROR: MethodError: `df_to_m` has no method matching
> df_to_m(::DataFrames.DataFrame, ::Type{Jinnie.Package})
> Closest candidates are:
> df_to_m(::DataFrames.DataFrame, ::Type{Jinnie.Jinnie_Model})
>
> How could the function be defined to work with the types itself (rather
> than instances) and be polymorphic as intended?
>
> Thanks for your time.
>
> Cheers
>
