Loop over array of static arrays

General Usage Performance
,
2

Yup. The following is about 7x faster for me:

function doubles_using_sarrays()
    xs = [@SVector(ones(10)) for i in 1:10]
    for i in 1:9
        xs[i+1] = double(xs[i])
        # Do some more stuff
    end
    xs
end

Key points:

  1. Don’t call ones(10) and then convert to a StaticArray. Not only does this first heap-allocate a ones(10) array before converting, but it is also type-unstable. The key to efficient use of StaticArrays is to let the compiler know the length of the array. The @SVector macro rewrites the ones(10) into a call to StaticArrays.ones((SVector){10}), which puts the length 10 in the type. — this is a common confusion, see e.g. Optimizing function with vector reassignments - #8 by stevengj
  2. Since SVector is immutable, use = instead of .=.

(The only remaining heap allocation is the container xs. You could use a static array for that as well, if you want, but as the size of the object increases the advantage of static arrays is less. And, again, you only get an advantage if you know the length at compile time. Does it really make sense in your application to make the length a constant?)