iterator interface

[tpapp]

Thanks for this great library, I find it very useful. However, I am not sure that the library supports the iteration interface of Julia. Eg Sobol.SobolSeq returns not an iterator, but an iterator and a state. So, for example,

import Sobol

function collect_take(iter, n)
    v = Vector{Float64}(0)
    for (i, x) in enumerate(iter)
        push!(v, x[1])
        if (i >= n)
            break
        end
    end
    v
end
double_take(iter, n) = vcat(collect_take(iter,5), collect_take(iter,5))
double_take(Sobol.SobolSeq(1), 5)

returns the first 10 elements (instead of the first 5, twice). Cf, for example,

double_take(countfrom(1),5)

Also, idioms like

[x[1] for x in take(Sobol.SobolSeq(1),5)]

don't work.

[stevengj]

In this case, the iterator is the state; it's not so easy to separate the two. Iterating twice on the same sobolseq object will given different numbers.

[x[1] for x in take(Sobol.SobolSeq(1),5)] not working seems to be a bug in take: I get ``MethodError: no method matching length(::Sobol.SobolSeq{1}), which means that take` only works on the subset of iterators supporting `length`. This seems like it should be fixed.

[stevengj]

Oh, looks like I need to define iteratorsize and some other optional methods.

[stevengj]

Seems like I got bit by JuliaLang/julia#15977.

[stevengj]

(Note that the take example now works.)

[tpapp]

If supporting iterate and functional style is a goal, then it could be done the following way:

1. SobolSeq{N} has no fields, just stores N,
2. x, state = iterate(::SobolSeq) allocates and returns in state what are now the fields of SobolSeq,
3. iterate(::SobolSeq, state) just updates state in place.