On 17/11/2010, at 8:24 PM, Devraj Mukherjee wrote:
> Does these two things mean the same?
>
> [myObject valueForString:@"param"] == [NSNull nul] ? @"X":@"Y"
> [myObject valueForString:@"param"] ? @"X":@"Y"
No.
First, I assume you mean -valueForKey:, not -valueForString:, plus it's +null,
not +nul. Pedantry aside, the comparisons are still not equivalent, even
allowing for the logical inversion you have introduced.
In the second case, @"X" will be chosen if the expression evaluates to true.
That will be when the value returned is NOT nil. In the first case, @"X" will
be chosen when the expression evaluates to equal the address (pointer) of the
object [NSNull null]. Since that's a real, concrete object, it will be some
valid address, not nil.
If you want @"X" to be chosen if the value is nil OR [NSNull null], then the
correct expression would be just that:
if([myObject valueForKey:key] == nil || [myObject valueForKey:key] == [NSNull
null])
return @"X";
else
return @"Y";
You could write this using the tertiary operator syntax, but since it's clearly
confusing you, I'd stick with if/else.
--Graham
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