This seems to work
(@view x.a[2:end]) .+= (@view y[2:end])
I’d call it an omission(bug). Macro programming is hard. Would suspect .+= isn’t recognized…
Edit: Hm. Seems to be more complicated, because
v1 = [1]
v2 = [2]
@views v1[begin:end] .+= v2[begin:end]
works. So parser precedence again(had this one time before…)?