Deprecate reverse_iter to Iterators.reverse

[nickrobinson251]

• trying out replacing reverse_iter with Iterators.reverse (not reverse since we don't promise to make a copy) -- thoughts?
• in the spirit of "No exported functions that could be just done with overloads of Base" (Maturing out the package (Path to DataStructures.jl v1.0) #479)
• as commented in Maturing out the package (Path to DataStructures.jl v1.0) #479, I don't think the Iterators.reverse(::T) -> Iterators.Reverse{T} is promised by the Iterators API, since it's not documented or tested for in Base (i.e. the changes of this PR don't break that API).

[oxinabox]

Seems like this is inline with the documentation for Base.Iterators.reverse

help?> Base.Iterators.reverse
  Iterators.reverse(itr)

  Given an iterator itr, then reverse(itr) is an iterator over the same collection but in the
  reverse order.

  This iterator is "lazy" in that it does not make a copy of the collection in order to reverse
  it; see Base.reverse for an eager implementation.

  Not all iterator types T support reverse-order iteration. If T doesn't, then iterating over
  Iterators.reverse(itr::T) will throw a MethodError because of the missing iterate methods for
  Iterators.Reverse{T}. (To implement these methods, the original iterator itr::T can be obtained
  from r = Iterators.reverse(itr) by r.itr.)

Iterators.reverse was implemented by @stevengj in JuliaLang/julia#24187
perhaps he can comment on if it is allowable to return something other than a Reverse{T}

I guess the question is particular for Stack which for its reverse would iterate reverse(reverse(::Deque)
so it makes sense to have it just iterate the Deque.
https://github.com/JuliaCollections/DataStructures.jl/pull/670/files#diff-7356e908345ca352e9d4e26734784cfeR56

[oxinabox]

I think this is a good idea.
Lets give it a few days for others to chime in, and if noone says it is a bad idea lets merge it,
after bumping the patch version

[nickrobinson251]

the question is particular for Stack which for its reverse would iterate reverse(reverse(::Deque)
so it makes sense to have it just iterate the Deque.
https://github.com/JuliaCollections/DataStructures.jl/pull/670/files#diff-7356e908345ca352e9d4e26734784cfeR56

Yeah. I wonder: even if it's okay for Iterators.reverse(::Stack) to return DequeIterator (rather than a Reverse{<:Stack}), perhaps the return should still implement all the methods that work on Iterators.Reverse, such as first and last? We'd need to add last for DequeIterator i think.

[stevengj]

perhaps he can comment on if it is allowable to return something other than a Reverse{T}

Absolutely. That's why it's called reverse(itr) and not Reverse(itr). For example, we already do:

julia> Iterators.reverse(1:10)
10:-1:1

[nickrobinson251]

^ just rebased to resolve merge conflicts

[oxinabox]

Merge and tag when ready.

[nickrobinson251]

i don't have permissions to do that. But feel free to give me them if you want. Or please merge and tag when you've the time

[oxinabox]

I gave you permissions several days ago.
I see you are still listed as pending accepting.
I think you can go to https://github.com/orgs/JuliaCollections/people
to accept.
or if not you'll need to find the email

[nickrobinson251]

ah, nice, thanks! i missed that email (i get too many GitHub email and need to fix that)
But i could see the invite by jsut going to https://github.com/JuliaCollections :)