On Feb 28, 2010, at 23:12, Eagle Offshore wrote:
> Documentation? "NSNull" does not appear in the documentation.
> http://developer.apple.com/mac/library/documentation/cocoa/reference/CoreDataFramework/Classes/NSManagedObject_Class/Reference/NSManagedObject.html
>
> NSNull is conceptually the wrapper for nil,
No, this is a false statement. See:
http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Classes/NSNull_Class/Reference/Reference.html
"The NSNull class defines a singleton object used to represent null values in
collection objects (which don’t allow nil values)."
Getting "the wrapper for nil" out of this is going a bit too far.
> like NSNumber is the wrapper for a number.
And this is a false statement (because of the word "like"). KVC has the
built-in ability to transform numeric property values to and from NSNumber
objects. There is no such behavior involving NSNull.
> It is conceptually inconsistent to treat them differently.
Therefore this is also a false statement. There is a certain superficial
similarity between nil/NSNull and number/NSNumber, perhaps, but that's about
all.
> NSMutableDictionary* dict = [NSMutableDictionary dictionary];
>
> [dict setObject: 5 forKey: @"foo"] // fails - must have object
> [dict setObject [NSNumber numberWithInt: 5] forKey: @"foo"]; // OK
>
> [dict setObject: nil forKey: @"bar"] // fails - must have object
> [dict setObject: [NSNull null] forKey: @"bar"]; // OK
>
> NSManagedObject* obj; // gets created somehow
>
> [obj setValue: nil forKey: @"bar"]; // succeeds where NSDictionary fails
> [obj setValue: [NSNull null] forKey: @"bar"]; // fails where NSDictionary
> succeeds
Of course it fails. '[dict setObject: ... forKey: @"bar"];' sets the object for
a key in a dictionary. '[obj setValue: ... forKey: @"bar"];' sets the value of
an object property. The two mechanisms are unrelated.
> so - this is conceptually buggy thinking and the thoughtful developer could
> be forgiven for being VERY SURPRISED by this behavior that is NOT DOCUMENTED.
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