I'd probably just do this:
type FieldObj{R}
data::Array{Float64, R}
meta::Dict{ASCIIString, Union(Int64, Float64)}
N::Int64
rank::Int64
function FieldObj(data::Array{Float64, R}, meta::Dict{ASCIIString, Union(
Int64, Float64)}=default_meta())
new(data, meta, size(data, R), R-2)
end
end
typealias ScalarField FieldObj{2}
typealias VectorField FieldObj{3}
You don't need all those definitions! You can combine your two outer
constructors using a default value for meta, and then if you're not going
to be using FieldObj itself as a constructor, there's no need for the outer
parametric constructor function, either.
julia> ScalarField(ones(100,100))
FieldObj{2}(100x100 Array{Float64,2}: …
julia> VectorField(ones(100,100))
ERROR: no method FieldObj{3}(Array{Float64,2})
Typically, I try not to define inner methods as the default ones are very
useful. But in this case, it may be what you're after.
On Thursday, June 19, 2014 1:14:40 PM UTC-4, Davide Lasagna wrote:
>
> HI,
>
> Coming from the Python world is a big step, especially when dealing with
> parametric types and their constructors. But Julia looks so promising and
> it is so fun to code with that i do not give up. I have an issue, though.
>
> Say I define the following parametric type:
> type FieldObj{R}
> data::Array{Float64, R}
> meta::Dict{ASCIIString, Union(Int64, Float64)}
> N::Int64
> rank::Int64
> function FieldObj(data::Array{Float64, R}, meta::Dict{ASCIIString,
> Union(Int64, Float64)})
> new(data, meta, size(data, R), R-2)
> end
> end
>
> function FieldObj{R}(data::Array{Float64, R}, meta::Dict{ASCIIString,
> Union(Int64, Float64)})
> FieldObj{R}(data, meta)
> end
>
> function FieldObj{R}(data::Array{Float64, R})
> FieldObj{R}(data, default_meta())
> end
> where the parameter R specifies the dimension of the array data. (Is this
> possible at all??)
>
> I can now instantiate objects as
> phi = FieldObj{2}(ones(100, 100))
> ok.
>
> However, i want to define some typealiases, to have a nicer interface,
> and because operators will have a different meaning for each R. Say the
> typealiases are:
> typealias ScalarField FieldObj{2}
> typealias VectorField FieldObj{3}
>
> With these aliases I cannot directly create new objects and I get
> julia> phi = ScalarField(ones(100, 100))
> ERROR: no method FieldObj{2}(Array{Float64,2})
>
> However, if I define explicitly the constructors for the typealiases this
> is possible, say I define:
> function ScalarField(data::Array{Float64, 2})
> FieldObj{2}(data, default_meta())
> end
> which works.
>
> Now, I have two questions:
> 1) Is there a way to avoid defining all the constructors explicitly by
> hand, say with an @eval block?
> 2) Why do I need to define these at all? What is "exactly" a typealias
> then?
>
> Thank you.
>
> Davide
>
>
>
>
>
>
