I'm not sure changing this behavior is possible,
at least not without making IOStream clonable.
And I suspect there are filesystem constraints against this.
Well there is a scary way, when the state just holds the current file
position,
then seeks to it when next is called,
reads a line,
then seeks back to where it was before.
So it looks like we are not mutating the underlying object.
(cos we undo our changes)
This would not be threadsafe though.
On Saturday, 23 April 2016 05:22:11 UTC+8, Dan wrote:
>
> Looks like it might be appropriate to make the `stream` in `Eachline` be
> the state of the iterator (instead of the `nada` returned by `next`).
>
> Opening an issue (perhaps with a PR of a fix) could be the next step.
> Unless someone finds some other logic for keeping `Eachline` the way it is.
>
> On Friday, April 22, 2016 at 7:09:13 AM UTC+3, Lyndon White wrote:
>>
>> I am writing some iterators that work with `IO`.
>>
>> I thought, so that my iterators would not mutate,
>> I would `deepcopy` the IO item, and store it as part of my state.
>> (then only my state would mutate, and no-one cares probably (unless they
>> were trying to `tee` for free))
>>
>> But `deepcopying` IO items apparently does not actually cause them to
>> become separate.
>> At least not for IOStreams.
>>
>>
>>
>> io=open("./data/text8/text8","r")
>> ia = deepcopy(io)
>> >IOStream(<file ./data/text8/text8>)
>>
>>
>> position(io)
>> >0
>>
>> position(seekend(io))
>> >100000000
>>
>> position(ia)
>> >100000000
>>
>>
>>
>> I was under the assumption that iterators never mutated, as there is no
>> `!` in `next`.
>> (then again there is also no `!` in `seekend`)
>>
>> So I was a bit stuck for how to implement.
>>
>> So I thought I would see how `Eachline` is implemented.
>> <https://github.com/JuliaLang/julia/blob/master/base/io.jl#L356>
>> It is mutating.
>> So maybe my assumptions are wrong, and iterators can be mutating?
>> They would be a lot easier to write that way, I guess.
>>
>> But julia does not have a `tee` function
>> <https://docs.python.org/2/library/itertools.html#itertools.tee>
>>
>>
>>
>>
