<< operator in objective c enum?

Question

I was looking for something and got in to this enum is apple UITableViewCell.h.

I am sorry if this is trivial but I wonder/curious what is the point of this.

I

Answer 1

It's a common trick in C to use the bitwise shift operator in enum values to allow you to combine enumeration values with the bitwise or operator.

That piece of code is equivalent to

enum {
    UITableViewCellStateDefaultMask                     = 0,
    UITableViewCellStateShowingEditControlMask          = 1, // 01 in binary
    UITableViewCellStateShowingDeleteConfirmationMask   = 2  // 10 in binary
};

This allows you to bitwise or two or more enumeration constants together

 (UITableViewCellStateShowingEditControlMask | UITableViewCellStateShowingDeleteConfirmationMask) // == 3 (or 11 in binary)

to give a new constant that means both of those things at once. In this case, the cell is showing both an editing control and a delete confirmation control, or something like that.