- style ▁mess aging . ▁ ▁Mess ages ▁The ▁Object ive - C ▁model ▁of ▁object - orient ed ▁programming ▁is ▁based ▁on ▁message ▁passing ▁to ▁object ▁instances . ▁In ▁Object ive - C ▁one ▁does ▁not ▁call ▁a ▁method ; ▁one ▁sends ▁a ▁message . ▁This ▁is ▁unlike ▁the ▁Sim ula - style ▁programming ▁model ▁used ▁by ▁C ++ . ▁The ▁difference ▁between ▁these ▁two ▁concepts ▁is ▁in ▁how ▁the ▁code ▁referenced ▁by ▁the ▁method ▁or ▁message ▁name ▁is ▁executed . ▁In ▁a ▁Sim ula - style ▁language , ▁the ▁method ▁name ▁is ▁in ▁most ▁cases ▁bound ▁to ▁a ▁section ▁of ▁code ▁in ▁the ▁target ▁class ▁by ▁the ▁compiler . ▁In ▁Small t alk ▁and ▁Object ive - C , ▁the ▁target ▁of ▁a ▁message ▁is ▁resolved ▁at ▁runtime , ▁with ▁the ▁receiving ▁object ▁itself ▁interpre ting ▁the ▁message . ▁A ▁method ▁is ▁identified ▁by ▁a ▁selector ▁or ▁ ▁— ▁a ▁unique ▁identifier ▁for ▁each ▁message ▁name , ▁often ▁just ▁a ▁- termin ated ▁string ▁representing ▁its ▁name ▁— ▁and ▁resolved ▁to ▁a ▁C ▁method ▁pointer ▁implementing ▁it : ▁an ▁. ▁A ▁consequence ▁of ▁this ▁is ▁that ▁the ▁message - pass ing ▁system ▁has ▁no ▁type ▁checking . ▁The ▁object ▁to ▁which ▁the ▁message ▁is ▁directed ▁— ▁the ▁receiver ▁— ▁is ▁not ▁guaranteed ▁to ▁respond ▁to ▁a ▁message , ▁and ▁if ▁it ▁does ▁not , ▁it ▁ra ises ▁an ▁exception . ▁ ▁S ending ▁the ▁message ▁ ▁to ▁the ▁object ▁pointed ▁to ▁by ▁the ▁pointer ▁ ▁would ▁require ▁the ▁following ▁code ▁in