objective c - ARC behavior on assigned local variable to an instance variable -

question 1

supposed have code:

myclass * __strong foo = [myclass new]; myclass * __strong bar = foo; // foo = nil; // arc? 

in reference this answer, arc automatically nil out foo on line 3 since bar acquired reference?

question 2

//ecgservice.m @property (strong) muttablearray *rridata;  (muttablearray *)getrridata {     return _rridata; }  //algorithmtest.m // according apple docs, local variable marked __strong default muttablearray *rridata = [self.ecgservice getrridata]; for(nsnumber *rri in rridata) {     // use rri! } // rridata = nil; 

should nil out local variable rridata after using it?

and, __strong attribute must applied 1 instance of object?

answer 1.

in principle, arc doesn't “nil out” foo until goes out of scope. when goes out of scope, arc releases reference. doesn't have set foo nil, effect if arc set nil.

in practice, arc allowed release reference held foo after last use of foo variable, may long before goes out of scope. in example, if place use foo in function in assignment bar, arc allowed release foo's reference after assignment. note there's no way know release because don't use foo again! note bar still reference object unless bar not used later in function.

there special attributes can prevent arc performing release, called objc_precise_lifetime , objc_returns_inner_pointer applied through macros ns_valid_until_end_of_scope , ns_returns_inner_pointer. these advanced features won't have worry time soon, if want see examples of ns_returns_inner_pointer, take @ nsstring.h.

answer 2.

you don't need “nil out” rridata. arc release reference when goes out of scope (or sooner—see answer 1).

you don't need __strong usually, because it's default, , it's want usually. normal have multiple strong references object. use __weak explicitly when need prevent retain cycle. there many explanations of retain cycles on web , on stack overflow, if need learn them, please visit favorite search engine.