▁( AR C ). ▁ ▁Object ive - C ▁on ▁iOS ▁ 7 ▁running ▁on ▁AR M 6 4 ▁uses ▁ 1 9 ▁bits ▁out ▁of ▁a ▁ 6 4 - bit ▁word ▁to ▁store ▁the ▁reference ▁count , ▁as ▁a ▁form ▁of ▁tag ged ▁pointers . ▁ ▁Properties ▁Object ive - C ▁ 2 . 0 ▁introdu ces ▁a ▁new ▁syntax ▁to ▁declare ▁instance ▁variables ▁as ▁properties , ▁with ▁optional ▁attributes ▁to ▁configure ▁the ▁generation ▁of ▁access or ▁methods . ▁Properties ▁are , ▁in ▁a ▁sense , ▁public ▁instance ▁variables ; ▁that ▁is , ▁declaring ▁an ▁instance ▁variable ▁as ▁a ▁property ▁provides ▁external ▁classes ▁with ▁access ▁( poss ibly ▁limited , ▁e . g . ▁read ▁only ) ▁to ▁that ▁property . ▁A ▁property ▁may ▁be ▁declared ▁as ▁" read only ", ▁and ▁may ▁be ▁provided ▁with ▁storage ▁semantics ▁such ▁as ▁assign , ▁copy ▁or ▁retain . ▁By ▁default , ▁properties ▁are ▁considered ▁atomic , ▁which ▁results ▁in ▁a ▁lock ▁prevent ing ▁multiple ▁threads ▁from ▁accessing ▁them ▁at ▁the ▁same ▁time . ▁A ▁property ▁can ▁be ▁declared ▁as ▁non atomic , ▁which ▁removes ▁this ▁lock . ▁ ▁@ interface ▁Person ▁: ▁NS Object ▁{ ▁ ▁@ public ▁ ▁NSString ▁* name ; ▁ ▁@ private ▁ ▁int ▁age ; ▁} ▁ ▁@ property ( copy ) ▁NSString ▁* name ; ▁@ property ( read only ) ▁int ▁age ; ▁ ▁-( id ) init With Age :( int ) age ; ▁@ end ▁ ▁Properties ▁are ▁implemented ▁by ▁way ▁of ▁the ▁@