view(::Memory, ::UnitRange) should not create a Vector

[MasonProtter]

I wasn't around to complain about #53896, but I think that PR was a bad idea. That PR made view worse at doing the regular job that view is used for, and repurposes it for a different job.

1. This now makes it so that generic functions that call

view(::AbstractVector, ::UnitRange)

might end up doing an unnecessary allocation depending on if you get a Memory (because Vector is a mutable struct). This means that any generic function that takes a view at every iteration of a loop is in danger of accidentally performing N allocations if it is passed a Memory. For example:

function f(v)
    s = 0.0
    for i ∈ firstindex(v):lastindex(v)-1
        s += sum(@view v[i:i+1])
    end
    s
end;

julia> let m = Memory{Float64}(undef, 10000) .= 1
           @btime f($m)
       end
  43.232 μs (9999 allocations: 312.47 KiB)
19998.0

julia> let v = Vector{Float64}(undef, 10000) .= 1
           @btime f($v)
       end
  10.129 μs (0 allocations: 0 bytes)
19998.0

2. If you actually wanted a regular SubArray{<:Memory}, you cannot use view for that and instead need to call the SubArray constructor directly

3. The only reason you'd want this to return a Vector instead of a SubArray is if you wanted to push! or otherwise resize the result, but it's generally not good practice to encourage people to write push!(view(m, idxs), x) because that'd normally error.

---

I propose we remove this method before 1.11 drops.

[KristofferC]

So what to do? Revert the wrap -> view PR and the wrap feature PR? Path of least resistance to me and 1.12 can be used to figure out exactly what to do.

[oscardssmith]

I think for 1.11, a good enough solution would be to revert wrap->view and unexport wrap. We do need an internal way of doing this, but we don't need a public interface.

[KristofferC]

We do need an internal way of doing this

We do? Julia seemed to work fine before #52049. I reverted both view and wrap on 1.11.

[jakobnissen]

Reverting sounds good to me for now. Also much less risky compared to adding a new function this late in the 1.11 release cycle.

[KristofferC]

#53192 makes a straight-up revert convoluted so I had to resort to just unexporting wrap in the end.

[JeffBezanson]

Looks like the decision has been made; removing triage tag.