On Apr 17, 2007, at 7:45 AM, Theodore H. Smith wrote:
>>>> Is it possible to not return an instance of a class from its
>>>> constructor?
>>>>
>>>> For example, say my constructor for SomeClass is:
>>>>
>>>> Sub Constructor(rs As RecordSet)
>>>> dim d As Date
>>>> dim fld As DatabaseField
>>>>
>>>> fld = rs.Field("EntryDate")
>>>> if fld = nil Then Return
>>>>
>>>> // assign values to class properties
>>>>
>>>> End Sub
>>>>
>>>> Instead of returning a useless instance of SomeClass with none of
>>>> its
>>>> properties filled to the method that called the constructor, it
>>>> would
>>>> be nice if it were possible to return a nil object. Is it
>>>> possible to
>>>> do that?
>>>
>>> You can do this the cocoa way:
>>>
>>> dim c as class1
>>> c = new class1
>>> c = c.Init
>>> // .Init may return nil
>>>
>>> In Cocoa, you can do this on one line, but it's still possible in
>>> RB,
>>> just not as stylish. Cocoa does it like this:
>>>
>>> MyNSClass* Result = [[bla alloc] init];
>>
>>
>> Here, alloc is a class method, and init is an object method.
>>
>>
>> Using a shared method in REALbasic does the same thing, also in one
>> line.
>>
>> dim c as Class1 = Class1.NewObject
>
> OK. What about if the user wants to override the init method?
>
> Like Class2 which subclasses from Class1?
>
> dim c as class1
> c = class2.NewObject.Init
>
> that would make it possible, right? Oh, is that only if Class2
> overrides Class1's NewObject function?
>
> You just can't do this in RB.
I think that I can, but so what?
>
> c = (new class2).Init
>
> Shame. It actually used to be possible sometime around RB 3 or 4 :)
Using a shared method to return a new object does not preclude
overriding of a constructor. But, ultimately, REALbasic and
Objective-C are very different languages. It does not bother me that
there are things that can be done in one but not the other, or that
some operations take more than one line of code to express.
Charles Yeomans
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