<< 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

These are bit-field flags. They are used because you can combine them using the bitwise-OR operator. So for example you can combine them like

(UITableViewCellStateShowingEditControlMask | UITableViewCellStateShowingDeleteConfirmationMask)

They work by having one bit set in an integer. In this example, in binary,

UITableViewCellStateShowingEditControlMask        = 0000 0001
UITableViewCellStateShowingDeleteConfirmationMask = 0000 0010

When they are OR'ed together, they produce 0000 0011. The framework then knows that both of these flags are set.

The << operator is a left-shift. It shifts the binary representation. So 1 << 1 means

0000 0001 shifted left by one bit = 0000 0010

1 << 2 would equal 0000 0100.