Re: Problem overriding a factory class mehtod
Re: Problem overriding a factory class mehtod
- Subject: Re: Problem overriding a factory class mehtod
- From: Ivan Kourtev <email@hidden>
- Date: Thu, 2 Nov 2006 21:53:20 -0500
On Nov 2, 2006, at 7:03 PM, Julien Jalon wrote:
It seems to be a "bad implementation" of FooA. I suppose +[FooA
fooWithInt:] implementation looks like:
+ (FooA *)fooWithInt:(int)someInt
{
return [[[FooA alloc] initWithInt:someInt] autorelease];
}
while it should be:
+ (id)fooWithInt:(int)someInt // don't strong type class creation
methods, it's generally a bad idea
{
return [[[self alloc] initWithInt:someInt] autorelease];
}
Yeah, I know but the actual initializer is quite more complex than
the example (although conceptually equivalent, I think).
FooA (the superclass) does have a designated initalizer
initWithX:y:z: -- so +[FooA fooWith***] looks like this:
+(id)fooWith***
{
// make x, y, z
return [[[FooA alloc] initWithX:x y:y z:z] autorelease];
}
Now I can replicate the x, y, z stuff into +[FooB fooWith***] and
have something like
+(id)fooWith***
{
// make x, y, z
return [[[FooB alloc] initWithX:x y:y z:z] autorelease];
}
which indeed works (or so it seems so far). But with this approach
there is code duplication so I thought maybe I am missing a more
elegant way to do this without duplicating code.
-- ivan
On 11/3/06, Ivan Kourtev <email@hidden> wrote:
I am faced with the following situation involving inheritance:
Class FooB inherits from class FooA. Class FooA implements a class
method
+ (FooA*)fooWithInt:(int)x;
The problem seems to arise with calls such as [FooB fooWithInt:x].
If I don't implement + [FooB fooWithInt], then I just get back a FooA
object (doesn't have FooB's variables).
If I override
+ (FooB*)fooWithInt:(int)x {
return [super fooWithInt:x];
}
then I get back a FooA object again.
So what is the "by-the-book" correct way to handle such situations?
I suppose a full reimplementation of + [FooB fooWithInt] (one that
doesn't call [super ...]) would do but then I am not able to reuse
the superclass's code. Not a problem in my case (I own all classes)
but what if I were working with another party's library and a header
file?
-- ivan
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