True, but when you care about performance it's much better to write the
wrapper functions---the results will be inferrable, unlike manipulations of
the parameters vector.
For Arrays, you already have the defined function `eltype` and `ndims`. If your
types fall into some kind of hierarchy, then you may be able to use subtyping.
For example:
julia> immutable MyWeirdArray{Sym,Len,T,N} <: AbstractArray{T,N}
data::NTuple{Len,T}
end
julia> ndims(MyWeirdArray{:zero_offset, 15, Float64, 1})
1
julia> eltype(MyWeirdArray{:zero_offset, 15, Float64, 1})
Float64
Both base/ julia and the ColorTypes package contain good examples of how to go
about this kind of manipulation.
Best,
--Tim
On Monday, February 15, 2016 05:28:19 AM Bart Janssens wrote:
> There is the parameters field of the types, but I'm not sure if that's
> considered private. You can do
> Array{Float64, 1}.parameters[2]
> to get 1, for example.
>
> On Monday, February 15, 2016 at 2:14:35 PM UTC+1, jw3126 wrote:
> > I have an instance of a parametric type, is there a canonical way to get
> > the parameter values?
> > For example I could have some Array{T, d} and want to know whether T is
> > Float64 and what its dimension is.
> > The only way of doing this I am aware of is writing code like:
> >
> > dimension{T, dim}(arr::Array{T, dim}) = dim
> > numbertype{T, dim}(arr::Array{T, dim}) = T
> >
> > Is there a built-in function to do this? And maybe a way to get parameter
> > values for arbitrary types?
> > E.g. I have some instance of MyType{S, T, U, n} is and want to know U. Do
> > I have to repeat code like the above each time I define a new parametric
> > type?
