Cyclic pair iterator?

General Usage Performance
2

You can just look at the docs and define methods required for iteration, see Interfaces · The Julia Language

Here is one implementation:

struct PairIterator{T}
    it::Vector{T}
end

# Required method
function Base.iterate(p::PairIterator, i::Int=1)
    l = length(p.it)
    if i > l
        return nothing
    else
        j = mod(i, l)+1
        return (p.it[i], p.it[j]), i+1
    end
end

# Important optional methods
Base.eltype(::Type{PairIterator{T}}) where {T} = Tuple{T,T}
Base.length(p::PairIterator) = length(p.it)

Example:

julia> for i in PairIterator([3,4,2,1])
           println(i)
       end
(3, 4)
(4, 2)
(2, 1)
(1, 3)
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