What is the meaning of this declaration? [closed]

Answer 1

This looks like Objective C and not C++, but regardless:

1 << 0

is just one bitshifted left (up) by 0 positions. Any integer "<<0" is just itself.

So

1 << 0 = 1

Similarly

1 << 1

is just one bitshifted left by 1 position. Which you could visualize a number of ways but the easiest is to multiply by 2.[Note 1]

So

x << 1 == x*2

or

1 << 1 == 2

Lastly the single pipe operator is a bitwise or.

So

1 | 2 = 3

tl;dr:

PKRevealControllerTypeNone  = 0
PKRevealControllerTypeLeft  = 1
PKRevealControllerTypeRight = 2
PKRevealControllerTypeBoth  = 3

[1] There are some limitations on this generalization, for example when x is equal to or greater than 1/2 the largest value capable of being stored by the datatype.