Question

I’m trying to add a convenience constructor to my custom object.
Similar to [NSArray arrayWithArray:]

I know it involves a class method that returns an auto released object. I’ve been googling around but all I can seem to find is the definition of a convenience constructor but not how to write one.

Answer 1

Let’s say you have the following:

@class PotatoPeeler : NSObject
- (instancetype)initWithWidget: (Widget *)w;
@end

Then to add a factory method, you’d change it to this:

@class PotatoPeeler : NSObject
+ (instancetype)potatoPeelerWithWidget: (Widget *)w;
- (instancetype)initWithWidget: (Widget *)w;
@end

And your implementation would simply be:

+ (instancetype)potatoPeelerWithWidget: (Widget *)w {
    return [[[self alloc] initWithWidget: w] autorelease];
}

Edit: replaced id with instancetype. They are functionally identical, but the latter provides better hints to the compiler about the method’s return type.