Synthesized Accessor Methods naming convention in Implementation file

[Rfields]

Since I'm using xcode 4.5 I decided to try leaving out the

@synthesize numerator, denominator; as the text says it is now no longer necessary (I have the @property int numerator,denominator; in the @interface file).

In the implementation file for the FractionTest example, if I do the following I get a ' Use of Undeclared identifier 'numerator'...'denominator' error:

@implementation Fraction

-(void) print
{
    NSLog(@"%i/%i", numerator,denominator);
}

@end

I have to either add the @synthesizer or change it to _numerator,_denominator.
Why do I need the underscore? the text says: 
In general, if you have a property called x, including the following line in your implementation section causes the compiler to automatically synthesize a getter method called x and a setter method called setX:

thank you

[afterDark]

The complete quote from the book is actually this:

In general, if you have a property called x, including the following line in your implementation section causes the compiler to automatically synthesize a getter method called x and a setter method called setX:.

@synthesize x;

So you need to explicitly use @synthesize if you want the instance variable name to be x. If you leave out the @synthesize directive, the 'standard' setter, getter and variable names will be used. Which means: variable names starting with an underscore _, as if you would have written:

@synthesize x = _x;

More explanation is in the Mac Developer Documentation ( https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/EncapsulatingData/EncapsulatingData.html , see under 'Most Properties are Backed by Instance Variables)

Unless you specify otherwise, the synthesized instance variable has the same name as the property, but with an underscore prefix. For a property called firstName, for example, the synthesized instance variable will be called _firstName.

Directly below that in the same document it says (under You can Customize Synthesized Variable Names)

As mentioned earlier, the default behavior for a writeable property is to use an instance variable called _propertyName.

If you wish to use a different name for the instance variable, you need to direct the compiler to synthesize the variable using the following syntax in your implementation:

@implementation YourClass

@synthesize propertyName = instanceVariableName;
...
@end

Admittingly, the case of what happens when you use @synthesize propertyName without the = is not discussed explicitly there.

In your code, you could for instance use

NSLog(@"%i,%i", self.numerator, self.denominator)

Sorry, a quite lengthy response... hope it helps!

[Rfields]

Thank you afterDark for taking the time to explain.