"shares memory with another argument" error from `reinterpret`ed `view`

[tkf]

Executing

buffer = zeros(UInt8, 4 * sizeof(Int))
mid = length(buffer) ÷ 2
x1 = reinterpret(Int, @view buffer[1:mid])
x2 = reinterpret(Int, @view buffer[mid+1:end])
x1 .= x2

throws:

ERROR: ArgumentError: an array of type Base.ReinterpretArray shares memory with another argument and must make a preventative copy of itself in order to maintain consistent semantics, but copy(A) returns a new array of type Array{Int64,1}. To fix, implement: Base.unaliascopy(A::Base.ReinterpretArray)::typeof(A)

I found that I can workaround it by unsafe_wrap:

buffer = zeros(UInt8, 4 * sizeof(Int))
mid = length(buffer) ÷ 2
y1 = reinterpret(Int, unsafe_wrap(Array, pointer(buffer, 1), mid))
y2 = reinterpret(Int, unsafe_wrap(Array, pointer(buffer, mid + 1),
                                  length(buffer) - mid))
y1 .= y2

But is there a less unsafe way to do it?

Note that a similar code using only view works:

z0 = collect(1:4)
z1 = @view z0[1:2]
z2 = @view z0[3:end]
z2 .= z1

so I suppose aliasing analysis can be done for reinterpreted view? If there is no safe way to do it, does it makes sense to add such feature?

[martinholters]

While figuring out that x1 and x2 actually don't alias would clearly be nice, doing what the error message suggests (implement Base.unaliascopy(A::Base.ReinterpretArray)::typeof(A)) should also be an option, no?

[tkf]

Yes, I agree. I just dug into the direction I was interested in.