"natural" ranges

[bjarthur]

natural in the sense of NaturalSort, where the step sizes are adjusted such that the elements come out in nice round numbers, like european currency. went looking, couldn't find a package, so quickly whipped up an iterator that would generate 1,2,5,10,20,50... would submit a PR here, but think perhaps this would best live elsewhere, perhaps on in it's own package. or did i miss sth somewhere? what do you think? i could see making another for 1,3,10,30,100,300...

_strip0(x) = (while x >= 10;  x = div(x,10);  end;  return x)
struct Range125{T} <: AbstractRange{T} 
    start::T
    stop::T
    function Range125(start, stop)
        in(_strip0(start), (1,2,5)) && in(_strip0(stop), (1,2,5)) || 
                error("start and stop must begin with 1, 2, or 5 and the rest of the digits if any must all be 0")
        new{typeof(start)}(start, stop)
    end 
end 
Base.first(r::Range125) = r.start
Base.last(r::Range125) = r.stop
Base.isempty(r::Range125) = first(r) > last(r)
Base.length(r::Range125) = round(Int, log10(last(r)/first(r))*3) + 1
Base.iterate(r::Range125) = isempty(r) ? nothing : (first(r), first(r))
function Base.iterate(r::Range125, s)
    s == last(r) && return nothing
    s0 = _strip0(s)
    n = if s0==2 
        div(5s,2)
    else
        2s
    end 
    (n, n) 
end 
function Base.show(io::IO, r::Range125{T}) where {T}
    print(io, "Range125{")
    show(io, T)
    print(io, "}(")
    ioc = IOContext(io, :typeinfo=>T)
    show(ioc, first(r))
    print(io, ", ")
    show(ioc, last(r))
    print(io, ')')
end
r=Range125(1,10)
@assert collect(r)==[1,2,5,10]

[mkitti]

I'm not sure if this is a very serious package. On one hand, we could pack everything here you would like. On the other hand, if you would like people to use it, they might like a dedicated package better.

[mkitti]

Is this really a range though? What makes a range an AbstractRange as opposed to an AbstractArray?