Make setscalar GPU-friendly

Author: blegat

src/sizes.jl

@@ -46,7 +46,12 @@ function _getscalar(x, sizes::Sizes, k::Int)
 end
 
 function _setscalar!(x, value, sizes::Sizes, k::Int)
-    return x[sizes.storage_offset[k]+1] = value
+    # Use a 1-element view + broadcast so this works on GPU storage as well as
+    # `Vector{Float64}`. Direct `x[idx] = value` is a scalar setindex which
+    # GPUArrays disallows by default.
+    pos = sizes.storage_offset[k] + 1
+    view(x, pos:pos) .= value
+    return value
 end
 
 function _getindex(x, sizes::Sizes, k::Int, j)