map

enum t0 = tuple(1, 2, 3);
static assert(map!(x => x)(t0) == t0);
enum t = tuple(1, 2, tuple(3, tuple(tuple(4, 5), 6), 7));
static assert(map!(x => x)(t) == t);

assert(map!(x => 2 * x)(t0) == tuple(2, 4, 6));
static assert(map!(x => 2 * x)(t) ==
              tuple(2, 4, tuple(6, tuple(tuple(8, 10), 12), 14)));

static assert(map!((int x, int y) => x + y)(tuple(1, 2)) == 3);
static assert(map!((int x, int y) => x + y)(
                  tuple(tuple(1, 2),
                        tuple(tuple(3, 4), tuple(5, 6))))
              == tuple(3, tuple(7, 11)));