@sdanisch, that is pretty advanced code and hard to grasp 
An alternative herein, using TensorCast.jl, which seems to use the same “black box technology” under the hood as StaticArrays, but thanks to a very logical and accessible syntax, one can get equivalent results in a more user-friendly way:
using TensorCast
@cast out2[i,j]{k} := vol[i,j,k]
NB: curly brackets allow different interpretation slices of the same memory, and assignment := returns views