BitArray - Is there one?

[Era Scarecrow]

 Curiously I'm making a huffman compression algo for fun, however 
I didn't see anything in std.array or anywhere that was to 
support bools specifically (in a packed form anyways). So I'm 
making one. So far I've got it saving the data as uint, 0 refers 
to the most significant bit and 7 the least significant, so A 
will come out as 0100001 and look right

 It supports a range, however foreach doesn't like using 
front/popFront/empty if I make opApply. It supports slices as 
well.

 For the BitArray, using it as follows I get an error:

struct BitArray {
  alias length opDollar;
  alias length __dollar;

  int length();
  Range opSlice();
  Range opSlice(int s, int e);
  struct Range {
     int opDollar();
  }
}

 BitArray ba = BitArray(someArrayOfUbyte);
 auto range = ba[0 .. $]; //needs to access 'this' for length? 
shouldn't it rewrite to ba[0 .. ba.opDollar()] ?
 auto range2 = ba[];      //works fine

 It also seems the BitArray (but not the range) requires __dollar 
rather than opDollar, however an alias seems to fix that. (Why is 
this?? the Range doesn't need a __dollar alias to work right)

 I also have it so you can ref the individual bools (by using an 
intermediate one in opApply). So..

//perfectly fine in unittest
foreach(ref r_b; range) {
  r_b = !r_b;
}