Oc,nil,null,nil,kcfnull

Yymodel Source has a sentence: Kcfnull

//parse the Model property and attach a value+ (Instancetype) yy_modelwithdictionary: (Nsdictionary *) Dictionary {if(!dictionary | | dictionary = = (ID) kcfnull)returnNil; if(! [Dictionary Iskindofclass:[nsdictionaryclass]])returnNil; Class CLS= [Selfclass]; //Parse class to get Modelmeta object_yymodelmeta *modelmeta =[_yymodelmeta Metawithclass:cls]; //Local class type mapping    if(modelmeta->_hascustomclassfromdictionary) {CLS= [CLS Modelcustomclassfordictionary:dictionary]?: CLS; } nsobject*one = [CLSNew]; //value-attached functions    if([one yy_modelsetwithdictionary:dictionary])returnOne ; returnNil;}

Nil:define the ID of a null instance, which points to a null pointer to an (instance) object

such as: nsstring *str = nil;

NSDate *date = nil;

Nil:defines the ID of a null class, pointing to a null pointer to a class

Class class = Nil;

NULL: Defines a null pointer for other types (base type, C type)

char *p = NILL;

NSNull: Placeholder for an element in an array, the element in the data cannot be nil (can be empty, that is, NSNull)

Cause: Nil is the end of the group ID

If nil is used, the number of k in the n array, the length of which is only a k element.

　　

A single case of Kcfnull:nsnull

There is a definition of kcfnull in corefoundation, which is actually a single case of NSNull

typedef const struct CF_BRIDGED_TYPE (NSNull) __cfnull *cfnullref;

Cf_export

Cftypeid Cfnullgettypeid (void);

Cf_export

Const CFNULLREF Kcfnull;//the Singleton NULL instance

NSNull *NULL1 = (id) kcfnull;

NSNull *null2 = [NSNull null];

Oc,nil,null,nil,kcfnull