import std.algorithm.comparison : equal;
import std.range : iota;

// positions 0, 2, 4 are set
auto b = BitArray([1, 0, 1, 0, 1, 0]);
b.flip();
// after flipping, positions 1, 3, 5 are set
assert(b.bitsSet.equal([1, 3, 5]));

bool[270] bits;
auto b1 = BitArray(bits);
b1.flip();
assert(b1.bitsSet.equal(iota(0, 270)));