`halve` silently fails on zip collections

[perrutquist]

The current implementation of halve(zip(xs...)) essentially amounts to zip(map(halve, xs)...). This causes a problem when halve splits collections differently. Each half is then a zip of different-length collections, and since zip stops iterating at the end of the shortest collection, some elements are silently left out.

[MasonProtter]

@perrutquist Can you check which version you're using? This is what I see currently:

julia> using SplittablesBase: halve

julia> halve(zip([1,2], [1,2,3]))
ERROR: ArgumentError: `halve(zip(...))` requires collections with identical `size`
Stacktrace:
 [1] shape
   @ ~/.julia/packages/SplittablesBase/FeYNd/src/implementations.jl:264 [inlined]
 [2] checkshape
   @ ~/.julia/packages/SplittablesBase/FeYNd/src/implementations.jl:258 [inlined]
 [3] halve(xs::Base.Iterators.Zip{Tuple{Vector{Int64}, Vector{Int64}}})
   @ SplittablesBase.Implementations ~/.julia/packages/SplittablesBase/FeYNd/src/implementations.jl:270
 [4] top-level scope
   @ REPL[5]:1

and it seems this was fixed back in 2020 by this PR: https://github.com/JuliaFolds/SplittablesBase.jl/pull/28/files

If you have an example on a recent version of SplittablesBase.jl where this still fails though, please let me know so we can think up a fix.

[perrutquist]

Here's an example of what I mean. Let Vector{Float64} be a stand-in for a user type, for which I define a halve method that cuts it "roughly in half".

(@v1.8) pkg> status SplittablesBase
Status `~/.julia/environments/v1.8/Project.toml`
  [171d559e] SplittablesBase v0.1.15

julia> import SplittablesBase: halve

julia> function halve(xs::Vector{Float64})
           mid = ceil(Int, length(xs)/2)
           left = @view xs[firstindex(xs):firstindex(xs)-1+mid]
           right = @view xs[firstindex(xs)+mid:end]
           return (left, right)
       end
halve (generic function with 20 methods)

julia> a = collect(1:5); b = float.(a);

julia> halve(zip(a,b))
(zip([1, 2], [1.0, 2.0, 3.0]), zip([3, 4, 5], [4.0, 5.0]))

julia> collect.(ans)
([(1, 1.0), (2, 2.0)], [(3, 4.0), (4, 5.0)])