nullable - Nonnull violation detection in Objective-C -

i have code declare object nonnull properties

@interface helloobject : nsobject @property (nonatomic,strong,nonnull) nsstring *foo; @property (nonatomic,strong,nonnull) nsstring *bar;  -(instancetype _nullable)initwithjson:(nonnull nsdictionary*)json; @end 

and initialize object json make use code:

-(instancetype _nullable)initwithjson:(nonnull nsdictionary*)json {     if( (self = [super init]) ) {         _bar = json[@"bar"];         _foo = json[@"foo"];     }      return self; } 

the server may have sent me malformed json. example, "foo" field might missing. easy enough check nil , return nil, have lot of code , inelegant , error prone.

is there easy , elegant way check see if object violates nonnull declarations @ runtime? example, don't want write code this:

        barx = json[@"bar"];         if (barx) {             _bar = barx;         } else {             return nil;         } 

that's ugly , boilerplate (and therefore prone error). i'd rather have like:

    if (![self validfornonnulls]) {         return nil;     } 

but can't think of way write validfornonnulls general object.

i don't think trying work around need test nil practical in objective-c.

if having verify many such incoming terms, , needed check them validity or return nil, rewrite initwithjson method check, category keep code clean , readable.

- (instancetype _nullable)initwithjson:(nonnull nsdictionary *)json {     if ( (self = [super init]) ) {         if ( ![json hasvaluesforkeys:@[@"foo", @"bar"]] ) {             //consider logging error             return nil;         }          _bar = json[@"bar"];         _foo = json[@"foo"];     }      return self; }  ...  @interface nsdictionary (hasvaluesforkeys) - (bool)hasvaluesforkeys:(nsarray *)keys; @end  @implementation  - (bool)hasvaluesforkeys:(nsarray *)keys {     (nsstring *key in keys) {         if ( !self[key] || [self[key] isequal:[nsnull null]] ) {             return no;         }     }      return yes; }  @end 

you make more specific tests each value if need validate whether nsnumber example.