Setting instance variables directly?

Question

This is a related question to one I posted earlier today, I was initially looking at how best to implement copyWithZone for an object that subclasses NSObject. I am pretty happy with what I have (see 001:) but wanted to ask about removing the setters (if it even matters, please say if its not really necessary).

It was pointed out to me that I could write:

newCrime->_title = [_title copyWithZone:zone];

I have two questions firstly, the -> is using C++ notation, is there an objective-c way of accessing a property of an object (without using a setter/dot notation)?

Finally, assign and strong how would I write those, I am pretty sure that assign would be:

newCrime->_coordinate = _coordinate;

but I am not sure about what to write for a strong pointer;

newCrime->_month =

.

@property(nonatomic, strong) NSString *month;
@property(nonatomic, strong) NSString *category;
@property(nonatomic, assign) CLLocationCoordinate2D coordinate;
@property(nonatomic, strong) NSString *locationName;
@property(nonatomic, copy) NSString *title;
@property(nonatomic, copy) NSString *subtitle;

.

// 001:
- (id)copyWithZone:(NSZone *)zone {
    Crime *newCrime = [[[self class] allocWithZone:zone] init];
    if(newCrime) {
        [newCrime setMonth:_month];
        [newCrime setCategory:_category];
        [newCrime setCoordinate:_coordinate];
        [newCrime setLocationName:_locationName];
        [newCrime setTitle:_title];
        [newCrime setSubtitle:_subtitle];
    }
    return newCrime;
}

Richard J. Ross III · Accepted Answer · 2012-03-28 16:26:09Z

2

-> is not C++ object notation, it is C pointer notation. Please get that C++ junk out of your head :)

As far as ARC is concerned, just have your variables defined in your interface as such:

@interface myObject : NSObject
{
    __strong strongIvar;
    __weak weakIvar;
    __unsafe_unretained assignIvar;
}

@end

And ARC will do the rest when you set the object using pointer notation (->).

For an example of pointer notation in pure C, look at the following example:

struct myStruct {
    int intMember;
    double doubleMember;
    char *stringMember;
};

#include <stdio.h>
#include <string.h>

int main(void) 
{
    struct myStruct *structVar = malloc(sizeof(myStruct));
    structVar->intMember = 10;
    structVar->doubleMember = M_PI * 2;
    structVar->stringMember = strdup("Hello World!");

    printf("%i %d %s", structVar->intMember, structVar->doubleMember, structVar->stringMember);

    free(structVar->stringMember);
    free(structVar);
}

answered Mar 28, 2012 at 16:26

Richard J. Ross III

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3 Comments

fuzzygoat Over a year ago

Thank you, my apologies with regards to C++, I was referring to -> in the OOP sense of accessing a member variable of an object. If you specify the variables as __strong __weak etc. in the @interface is it then sufficient to just directly assign them afterwards i.e. newCrime->_month = _month; ?

Richard J. Ross III Over a year ago

@fuzzygoat yes, ARC will add retain / release cycles as necessary. But note that copy properties will need to be strong and assigned by using the -copy selector.

fuzzygoat Over a year ago

Thank you, much appreciated Richard, I am guessing that with respect to my copyWithZone implementation that I would want to assign copy properties using -copyWithZone?

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