DOT-NOTATION Confusing me

[iphone.savvy]

HI EXPERTS,

I have a class A in which i have declared some variable 'var' in the header file and have property for that Variable.
In Class B i have an instance of Class A and through which i am calling 'var' .
Calling variable like below,
aClassObject.var , it gives me an error , but in many ways i noticed variable calling using Dot.

And When i call as follows,
[aObject var] No ERROR and NO WARNING.
This is confusing me call the messages using square brackets but it is also calling variable.
Can anyone of you just put some light on this?

[iphone.savvy]

When we can call the messages with the dot notation.
Ex:
@interface A:NSObject
{
NSString *text;
}
-(void)initialise;
@end

@implementation A
-(void)initialise {
text = @"Hello Viewer";
}

...Now inside the method of class B
(void)doSomething
{
A *aObj = [[A alloc]init];
aObj.initialise; //Works Fine
[aObj initialise]; // Works Fine

So why can't we create an instance of A like below,
A *aObj = A.alloc.init;

Why? Any Thoughts?

[Duncan C]

Originally Posted by iphone.savvy

HI EXPERTS,

I have a class A in which i have declared some variable 'var' in the header file and have property for that Variable.
In Class B i have an instance of Class A and through which i am calling 'var' .
Calling variable like below,
aClassObject.var , it gives me an error , but in many ways i noticed variable calling using Dot.

And When i call as follows,
[aObject var] No ERROR and NO WARNING.
This is confusing me call the messages using square brackets but it is also calling variable.
Can anyone of you just put some light on this?

You need to read up on properties.

When you declare an @property in your header, you are telling the system that you will create a setter and a getter method that can be used to read or write values to the instance variable that is used to save that property's variable.

When you add an @synthesize statement, the compiler generates a setter and a getter method for your property:

the getter

- (type) var;

The setter:

- (void) setVar;

When you use code like this:

anotherVar = anObject.var;

The compiler recognizes this as a property reference. If you haven't declared a property, the compiler generates an error.


The statement

anotherVar = [anObject var];

is an explicit call to the getter method.

The compiler will generate a WARNING (not an error) if it can't find that method. That's because method calls are resolved at runtime. If there is a method with that name at runtime, the code will work. If not, it will crash.

In order for class A to refer to a property of class B, the .m file for class A needs to #import the header of class B. My guess is that you forgot that step, and that you actually got a warning when you first compiled your code. If you select clean from the project menu and rebuild, I bet you'll see a warning about an unknown method for that call.