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Deya Eldeen Elkhawaldeh 
Deya Eldeen Elkhawaldeh
iOS Engineer SDE III @ Expedia Group
Published Jan 7, 2022
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As a programmer, sometimes you will need to define “nothingness”… 🧐
Data stores can have a value, or simply be nothing, thisnothingcomes in different flavors (nil, Nil, Null, NSNull) which all came to be called “null”.
In Swift, you will not be able to deal directly with NULL and Nil,
say you have this code in Objective C
// Machine.h#import <Foundation/Foundation.h>@interface Machine : NSObject@property (strong, nonatomic) id serialNumber;- (void) summary;@end// Machine.m#import <Foundation/Foundation.h>#import "Machine.h"@implementation Machine- (void) summary { NSLog(@"Initializing Machine"); NSString *label1 = @"label1"; NSString *label2 = nil; NSString *label3 = [NSNull null]; NSString *label4 = Nil; NSString *label5 = NULL; NSLog(@"Label1 = %@",label1); NSLog(@"Label2 = %@",label2); NSLog(@"Label3 = %@",label3); NSLog(@"Label4 = %@",label4); NSLog(@"Label4 = %@",label5);}@end after preparing the bridging header, you will be able to create Machine Objects
let OC_Machine = Machine()OC_Machine.summary()OC_Machine.serialNumber = 21OC_Machine.serialNumber = nilOC_Machine.serialNumber = NSNull()//OC_Machine.serialNumber = Nil//OC_Machine.serialNumber = Nullprint(OC_Machine.serialNumber) As you can see, the commented lines will not compile in swift, but should be running ok in Objective C, you will see this output
Label1 = label1
Label2 = (null)
Label3 = <null>
Label4 = (null)
Label4 = (null)
Optional(<null>)
[NSNull null] is a wrapper for nil
nilis defined as :#define nil NULLand is Objective C equivalent for CNULL
Nil is for object pointers, NULL is for non pointers, Null and Nil both defined to be equal to the value zero.
NULLis avoid *,nilis anid, andNilis a Class pointer,NULLis used fornon-object pointer(like a C pointer) in Objective-C. Likenil,NULLgot no value nor address (used to check if a struct is empty).
Keep in mind these quotes:
In Objective-C: nil is a pointer to a non-existent object.
In Swift: nil is not a pointer, it’s the absence of a value of a certain type.
NULL and nil are equal to each other, but nil is an object value while NULL is a generic pointer value ((void*)0, to be specific).[NSNull null]is an object that’s meant to stand in for nil in situations where nil isn’t allowed. For example, you can’t have a nil value in an NSArray. So if you need to represent a “nil”, you can use[NSNull null].
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Deya Eldeen Elkhawaldeh
iOS Engineer SDE III @ Expedia Group
2y
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💡: I have updated this article, it had some alignment missed up.
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