ustrip of a view cannot be assigned to :(

[bjarthur]

i need to send a unitful array into LinearAlgebra.BLAS.symv! as the last argument (i.e. the one assigned to). so i tried ustrip and that works if i use it on the entire array. but the tricky bit is that i just want to input a portion of it, and to be fast and efficient with memory, would like to use a view. i'm finding that a ustrip of a view cannot be assigned to. what follows is a minimal example without symv. is there a way to make this work without allocation? thx.

julia> v = zeros(3) * 1u"kg"
3-element Vector{Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}}:
 0.0 kg
 0.0 kg
 0.0 kg

julia> vv = @view v[1:2]
2-element view(::Vector{Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}}, 1:2) with eltype Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}:
 0.0 kg
 0.0 kg

julia> ustrip(vv)[1] = 1    # seems to work, but...
1

julia> vv     # nope, it actually doesn't
2-element view(::Vector{Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}}, 1:2) with eltype Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}:
 0.0 kg
 0.0 kg

julia> v     # not updated here either
3-element Vector{Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}}:
 0.0 kg
 0.0 kg
 0.0 kg

julia> ustrip(v)[1] = 1    # but without the view....
1

julia> v     # it works just fine
3-element Vector{Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}}:
 1.0 kg
 0.0 kg
 0.0 kg

[bjarthur]

doh, okay, to answer my own question just 20 min later, you just reverse the composition and take a view of a ustrip. so, continuing from the example above:

julia> uv = ustrip(v)
3-element reinterpret(Float64, ::Vector{Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}}):
 1.0
 0.0
 0.0

julia> vuv = @view uv[1:2]
2-element view(reinterpret(Float64, ::Vector{Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}}), 1:2) with eltype Float64:
 1.0
 0.0

julia> vuv[1]=2
2

julia> vuv
2-element view(reinterpret(Float64, ::Vector{Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}}), 1:2) with eltype Float64:
 2.0
 0.0

julia> uv
3-element reinterpret(Float64, ::Vector{Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}}):
 2.0
 0.0
 0.0

julia> v
3-element Vector{Quantity{Float64, 𝐌, Unitful.FreeUnits{(kg,), 𝐌, nothing}}}:
 2.0 kg
 0.0 kg
 0.0 kg