Question

Please consider the following two initialization methods.

The first method simply passes the value of the parameters to their respective NSString properties, but the second allocates the properties and then initializes them using the initWithString: method. Is the allocation in the latter example necessary?

Thanks in advance.

-(id)initWithTitle:(NSString *)theTitle muscleGroup:(NSString *)theMuscleGroup equipment:(NSString *)theEquipment {
    if((self = [super init])){  
        title = theTitle; 
        muscleGroup = theMuscleGroup; 
        equipment = theEquipment; 
    }
    return self; 
}

-(id)initWithTitle2:(NSString *)theTitle muscleGroup:(NSString *)theMuscleGroup equipment:(NSString *)theEquipment {
    if((self = [super init])){  
        title = [[NSString alloc] initWithString:theTitle]; 
        muscleGroup = [[NSString alloc] initWithString:theMuscleGroup]; 
        equipment = [[NSString alloc] initWithString:theEquipment];  
    }
    return self; 
}

Answer 1

The first example is not safe because you are not taking ownership of the strings, so your program will get all crashy if they are later released elsewhere. The second example fixes that problem and will work perfectly well, but is more concisely written thusly:

-(id)initWithTitle2:(NSString *)theTitle muscleGroup:(NSString *)theMuscleGroup equipment:(NSString *)theEquipment {
    if((self = [super init])){  
        title = [theTitle copy]; 
        muscleGroup = [theMuscleGroup copy]; 
        equipment = [theEquipment copy];  
    }
    return self; 
}

NSString gives you a copy constructor (-initWithString:), which enables you to do what you are doing in #2, but not all classes do. copy requires the class to implement the NSCopying protocol, but is more conformant with the way a Cocoa API developer would expect to be able to copy objects.