$(D_KEYWORD true) if r1 and r2 have the same head, $(D_KEYWORD false) otherwise.
const int[2] array; auto r1 = array[]; auto r2 = array[]; assert(sameHead(r1, r2));
const int[2] array; auto r1 = array[]; auto r2 = array[1 .. $]; assert(!sameHead(r1, r2));
Determines whether r1.front and r2.front point to the same element.