ios - What happens if we don't check for "if (self)" in init methods? -

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• in objective-c why should check if self = [super init] not nil? 9 answers

i started code done our senior, found init method have code -(id)init method. used code following ways. code below used viewcontrollers.

    self = [super initwithnibname:@"viewcontroller" bundle:[nsbundle mainbundle]];     return self; 

what use of if(self) , self in part?

    //and in viewcontroller contains.     self = [super initwithnibname:@"viewcontroller" bundle:[nsbundle mainbundle]];     if (self) {         //do stuff     }     return self; 

when access instance variables in methods code equivalent addressing them via self pointer:

- (void)method {   ivar = 1;   // following line executed:   self->ivar = 1; } 

so if reason self pointer nil , access ivars in init method, application crash try derefenrence null pointer. e.g. following simple example crash:

@implementation testobj {   int a; }  - (id) init {   self = [super init];   self = nil;    = 1; // crash   return self; } @end 

also if [super init] method returned nil reason, might indicator went wrong , should not proceed object initialization , other required work it.