More exact reason is that Base.alignment iterates the rows of a vector or matrix to find the space needed to print all the elements in an aligned column, then Base.print_matrix_row iterates again to print. Each iteration indexes a few times, the exact number varying by version, so it’s not good to print while indexing. I’d separate the printing step from the element computation, and write a method (function (s::SomeVec)(i::Int)...) for SomeVec instances so a just-as-concise call init(i) prints while indexing init[i] doesn’t.