instance-variables

Here is some code: class Person def initialize(age) @age = age end def age @age end def age_difference_with(other_person) (self.age - other_person.age).abs end protected :age end What I want to know is the difference between using @age and self.age in age_difference_with method. Writing @age directly accesses the instance variable @age . Writing self.age tells the object to send itself the message age , which will usually return the instance variable @age — but could do any number of other things depending on how the age method is implemented in a given subclass. For example, you might have a

What are Ruby variables preceded with double at signs ( @@ )? My understanding of a variable preceded with an at sign is that it is an instance variable, like this in PHP: PHP version class Person { public $name; public function setName($name) { $this->name = $name; } public function getName() { return $this->name; } } Ruby equivalent class Person def set_name(name) @name = name end def get_name() @name end end What does the double at sign @@ mean, and how does it differ from a single at sign? A variable prefixed with @ is an instance variable , while one prefixed with @@ is a class variable .

I tend to use properties exclusively in my classes, especially now that you can declare properties in a class extension thanks to the modern Objective-C 2.0 runtime—I use this feature to create "private" properties. My question is if there is any good reason to ever declare ivars in a class interface anymore. I prefer my public-facing interfaces to be as minimal and clean as possible, only revealing aspects of my class that are pertinent. For example, I would tend to do the following: MyClass.h : @interface MyClass : NSObject @property (nonatomic, copy) NSString * publicString; @property

What is the difference between a static and instance variable. The following sentence is what I cant get: In certain cases, only one copy of a particular variable should be shared by all objects of a class- here a static variable is used. A static variable represents class wide info.All objects of a class share the same data. I thought that instance vars were used class wide whereas static variables only had scope within their own methods? In the context of class attributes, static has a different meaning. If you have a field like: private static int sharedAttribute; then, each and every