If you're type has only concrete field then it will be densely packed
regardless of wether it's immutable or not.
On Tuesday, 3 March 2015 17:15:20 UTC, Mauro wrote:
>
> > Mauro, I do not quite understand what you're saying about densely packed
> > arrays, could you explain a bit more?
>
> Consider:
>
> julia> immutable A
> x::Float64
> y::Float64
> end
>
> julia> type B
> x::Float64
> y::Float64
> end
>
> julia> a = [A(4,5), A(5,6)]
> 2-element Array{A,1}:
> A(4.0,5.0)
> A(5.0,6.0)
>
> julia> b = [B(4,5), B(5,6)]
> 2-element Array{B,1}:
> B(4.0,5.0)
> B(5.0,6.0)
>
> Then in memory `a` is actually identical to:
>
> [4., 5., 5., 6.]
>
> (or
> [4. 5.; 5. 6.] )
>
> As Julia knows that the type of `a` is Vector{A}, it knows how to
> interpret that junk of memory. Conversely, `b` is a vector of pointers
> which point to the two instances of `B`. So, working with b is slower
> than an Array{Float64,2} whereas a should be just as fast.
>
> > Thanks,
> > Chris
> >
> > On Tuesday, March 3, 2015 at 11:41:53 AM UTC-5, Mauro wrote:
> >>
> >> > I believe if all your type fields are concrete (which they are in the
> >> case
> >> > of Float64), the performance should be the same as using
> >> Vector{Float64}.
> >> > This is really nice since you get to use code that is much more
> >> > understandable like state.x instead of state[1] for no penalty.
> >>
> >> I think to get densely packed array the type needs to be immutable:
> >>
> >> immutable StateVec
> >> x::Float64
> >> y::Float64
> >> z::Float64
> >> end
> >>
> >> Otherwise it will be an array of pointers.
> >>
>
>
