How to use `iterate(s::Stack)` and `Iterators.reverse(s::Stack{T})` for Stack and Queue in DataStructures.jl?

New to Julia
1

I am reading documentation for DataStructures.jl, namely this page: Stack and Queue · DataStructures.jl and cannot figure out how to use iterate(s::Stack) and Iterators.reverse(s::Stack{T})?

I try this:

s = Stack{Int}()
for i ∈ 1:5
    push!(s,i)
end

for i ∈ iterate(s)
    println(i)
end

and getting something that I don’t understand:

5
(DataStructures.DequeBlock{Int64}(capa = 1024, front = 1, back = 5): [1, 2, 3, 4, 5], 4)

How to iterate properly?

2

You don’t need iterate here:

julia> for i ∈ s
           println(i)
       end
5
4
3
2
1

julia> for i ∈ Iterators.reverse(s)
           println(i)
       end
1
2
3
4
5
3 
for i ∈ Iterators.reverse(s)
    println(i)
end

gives an error

MethodError: no method matching iterate(::Base.Iterators.Reverse{Stack{Int64}})
4

What version of DataStructures.jl are you using? It looks like support for Iterators.reverse was added in version 0.18.4. You can find out what version you are running with ] st DataStructures in the REPL.

2 Likes
5

It seems strange to me that Stack would support Iterators.reverse, one of the defining characteristic of a Stack is only allowing access to the top element.

6

v0.17.20, Julia 1.5.3 How to update DataStructures to the latest in REPL? up DataStructures does not update it.

7

Most likely, that means some other package is holding it back (by having it as a dependency, restricted to v0.17). Can you try add DataStructures@0.18?

2 Likes
8

Thanks! It works. First it gave me the error: ERROR: Unsatisfiable requirements detected for package Lasso. I don’t need Lasso for now, so I removed it, then add DataStructures@0.18 updated it to v0.18.9