"Small vector" optimization for Rust: store up to a small number of items on the stack
use smallvec::{SmallVec, smallvec};
// This SmallVec can hold up to 4 items on the stack:
let mut v: SmallVec<[i32; 4]> = smallvec![1, 2, 3, 4];
// It will automatically move its contents to the heap if
// contains more than four items:
v.push(5);
// SmallVec points to a slice, so you can use normal slice
// indexing and other methods to access its contents:
v[0] = v[1] + v[2];
v.sort();