Ruby natively supports class variables in modules, so you can use class variables directly, and not some proxy or pseudo-class-variables: module Site @@name = “StackOverflow” def self.setName(value) @@name = value end def self.name @@name end end Site.name # => “StackOverflow” Site.setName(“Test”) Site.name # => “Test”
Instead of bar use self.bar or Foo.bar. Assigning to Foo.bar will create a static variable, and assigning to self.bar will create an instance variable.
Variables declared inside the class definition, but not inside a method are class or static variables: >>> class MyClass: … i = 3 … >>> MyClass.i 3 As @millerdev points out, this creates a class-level i variable, but this is distinct from any instance-level i variable, so you could have >>> m = MyClass() >>> … Read more
Upcasting is casting to a supertype, while downcasting is casting to a subtype. Upcasting is always allowed, but downcasting involves a type check and can throw a ClassCastException. In your case, a cast from a Dog to an Animal is an upcast, because a Dog is-a Animal. In general, you can upcast whenever there is … Read more
A very interesting find. To understand it we need to dig into the Java Language Specification (JLS). The reason is that final only allows one assignment. The default value, however, is no assignment. In fact, every such variable (class variable, instance variable, array component) points to its default value from the beginning, before assignments. The … Read more
A variable prefixed with @ is an instance variable, while one prefixed with @@ is a class variable. Check out the following example; its output is in the comments at the end of the puts lines: class Test @@shared = 1 def value @@shared end def value=(value) @@shared = value end end class AnotherTest < … Read more
Instance variable on a class: class Parent @things = [] def self.things @things end def things self.class.things end end class Child < Parent @things = [] end Parent.things << :car Child.things << :doll mom = Parent.new dad = Parent.new p Parent.things #=> [:car] p Child.things #=> [:doll] p mom.things #=> [:car] p dad.things #=> [:car] … Read more
Variables declared inside the class definition, but not inside a method are class or static variables: >>> class MyClass: … i = 3 … >>> MyClass.i 3 As @millerdev points out, this creates a class-level i variable, but this is distinct from any instance-level i variable, so you could have >>> m = MyClass() >>> … Read more