All of the vector operations return new vectors instead of mutating. func v3_add (a, b v3) v3 { return v3{x: a.x + b.x, y: a.y + b.y, z: a.z + b.z}

All of the vector operations return new vectors instead of mutating. func v3_add (a, b v3) v3 { return v3{x: a.x + b.x, y: a.y + b.y, z: a.z + b.z} } A sensible approach for maintainable code but without knowing if a and b are used elsewhere the compiler can't reuse the space they occupy. If C can't figure it out, it can just stick a new one on the stack which doesn't cost too much. This is, of course, Rust's bread and butter which is probably why it takes the top spot.