▁Ne XT ▁was ▁" obj c 4 ". ▁This ▁project ▁name ▁was ▁kept ▁in ▁the ▁last ▁release ▁of ▁legacy ▁Object ive - C ▁runtime ▁source ▁code ▁in ▁Mac ▁OS ▁X ▁Leop ard ▁( 1 0 . 5 ). ▁ ▁Gar bage ▁collection ▁Object ive - C ▁ 2 . 0 ▁provided ▁an ▁optional ▁conserv ative , ▁gener ational ▁garbage ▁collect or . ▁When ▁run ▁in ▁backwards - compatible ▁mode , ▁the ▁runtime ▁turned ▁reference ▁counting ▁operations ▁such ▁as ▁" ret ain " ▁and ▁" release " ▁into ▁no - ops . ▁All ▁objects ▁were ▁subject ▁to ▁garbage ▁collection ▁when ▁garbage ▁collection ▁was ▁enabled . ▁Reg ular ▁C ▁pointers ▁could ▁be ▁qualified ▁with ▁" __ strong " ▁to ▁also ▁trigger ▁the ▁underlying ▁write - bar rier ▁compiler ▁intercept s ▁and ▁thus ▁particip ate ▁in ▁garbage ▁collection . ▁A ▁zero - ing ▁weak ▁sub system ▁was ▁also ▁provided ▁such ▁that ▁pointers ▁marked ▁as ▁" __ weak " ▁are ▁set ▁to ▁zero ▁when ▁the ▁object ▁( or ▁more ▁simply , ▁GC ▁memory ) ▁is ▁collected . ▁The ▁garbage ▁collect or ▁does ▁not ▁exist ▁on ▁the ▁iOS ▁implementation ▁of ▁Object ive - C ▁ 2 . 0 . ▁Gar bage ▁collection ▁in ▁Object ive - C ▁runs ▁on ▁a ▁low - p riority ▁background ▁thread , ▁and ▁can ▁halt ▁on ▁user ▁events , ▁with ▁the ▁intention ▁of ▁keeping ▁the ▁user ▁experience ▁respons ive . ▁ ▁Gar bage ▁collection ▁was ▁deprecated ▁in ▁Mac ▁OS ▁X ▁v 1 0 . 8 ▁in ▁favor ▁of ▁Autom atic ▁Reference ▁Count ing