<< operator in objective c enum? - objective-c

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 know the << from ruby but I don't really understand this enum ?
enum {
UITableViewCellStateDefaultMask = 0,
UITableViewCellStateShowingEditControlMask = 1 << 0,
UITableViewCellStateShowingDeleteConfirmationMask = 1 << 1
};
Thanks
BTW
Found it as a great way to learn coding, I am trying once in a day to get into the header files of at list on object.
Shani

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.

Answer 2

Its actually BItwise shift operator
<< Indicates the bits are to be shifted to the left.
>> Indicates the bits are to be shifted to the right.
So in your statement the value of 1 << 0 is 1 and 1 << 1 is 2

Answer 3

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.

Answer 4

These operand called bitshift. Bitshift operand can be preferred for
2 reasons.
- For fast operation
- Use multiple bool value in one time.
For example : 1<<2 is a left shift; that means
1 : 0001,
2 : 0010
1 << 2 this line means is 2 should be left one bit. As a result 0010 shifted to 0100
Also shifted value must ordered as a 1,2,4,8,16...
typedef NS_OPTIONS(int, EntityEngineer) {
EntityEngineeriOS = 1 << 0,
EntityCategoryAndroid = 1 << 1,
EntityCategoryDB = 1 << 2,
EntityCategoryTeamLead = 1 << 16,};
Now, we want to check mutiple boolean in below line,
char engineer = (EntityEngineeriOS | EntityCategoryAndroid);
char 0011 = (0001 | 0010);
if (engineer & EntityEngineeriOS) {
NSLog(#"we are looking for a developer who can write objective c or java");
}
if (engineer & EntityCategoryDB) {
NSLog(#"we are not looking for a DB manager");
}
Result : we are looking for a developer who can write objective c or java

Answer 5

That is the bitshift operator. That is used commonly for objects that may have multiple behaviors (each enum being a behavior).
Here is a similar post that may clarify it better.

Answer 6

These types of operator are called bitwise operator which operates on bit value of a number. These operation are very fast as compared to other arithematic operations.