[julia-users] Parametric Types with Incomplete Initialization

[Christopher Alexander]

Let's say I have the following types:

abstract ABC

type A <: ABC
        a::Float64
end

type B{T <: ABC}
        a::T
end

In some cases, I need for type "B" to be incompletely initialized so that I 
can define its parameter "a" later.  I've found out that you can do 
something like this:

type B{T <: ABC}
        a::T
        
        call(::Type{B}) = new{ABC}()
end

which then allows this:

julia> myB = B()
B{ABC}(#undef)

My question is, I'm assuming you lose any of the performance gain by using 
the parametric type in this case because you are still using the abstract 
type "ABC" for the parameter "a" (even if you define it later with a 
concrete "A").   Is there a better way to do this?

Thanks!

Chris