Making a no parameter type have "defaults"

Question

I essentially want to do the following:

typealias CVODE_BDF CVODE_BDF{:Newton,:Dense}

that is, allow a user to pass to my function CVODE_BDF and, if they did not set any of the type parameters, interpret it as CVODE_BDF{:Newton,:Dense}. I know that the typealias doesn't actually work, but is there a way to simulate this? Like in the function, read T.parameters[1] and somehow see that it was empty?

Answer 1

You can do this if the function accepts objects of that type, rather than the type itself. E.g.

type MyObject{T}
end


const DefaultMyObject = MyObject{Int64}()

f{T}(x::MyObject{T}=DefaultMyObject) = T

f(), f(MyObj{Float64}())

gives

(Int64,Float64)