Still not sure though how to go about using the actual types as params,
rather than an instance of that type.
sâmbătă, 27 februarie 2016, 14:56:47 UTC+1, Adrian Salceanu a scris:
>
> 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
>>
>
