concat

debug scope(failure) writefln("unittest Failure :%s(%s)", __FILE__, __LINE__);
debug scope(success) {writefln("Unittest Success :%s(%s)", __FILE__, __LINE__); stdout.flush();}

int[][] r1 = [[0, 1, 2, 3], [4, 5, 6], [7, 8], [9], []];
auto c = concat(r1);
assert(equal(c, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]));
assert(equal(c.retro(), retro([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]))); // bidir range
assert(equal(c.retro.retro, c));

assert(equal(concat(c), c));

auto r2 = [0, 1, 2, 3, 4, 5];
assert(equal(r2.map!"[a, 2]".concat, [0, 2, 1, 2, 2, 2, 3, 2, 4, 2, 5, 2]));
assert(equal(r2[0 .. 4].map!(a => repeat(a, a)).concat, [1, 2, 2, 3, 3, 3]));
assert(equal(r2[0 .. 3].repeat(2).map!(map!"a + 1").concat, [1, 2, 3, 1, 2, 3]));

int[] emp;
assert(emp.repeat(15).concat.empty);
assert(emp.concat.empty);