instance-variables

Is there any reason to declare a private ivar in @interface instead of @implementation ? I see code like this all over the internet (including documentation provided by Apple ): Foo.h @interface Foo : NSObject { @private id _foo; } @end Foo.m @implementation Foo // do something with _foo @end The header file defines the public interface of a class, whereas a private ivar is... well... private. So why not declare it like this? Foo.h @interface Foo : NSObject @end Foo.m @implementation Foo { @private id _foo; } // do something with _foo @end Declaring instance variables in the @implementation is

I have a class something like below, and I used instance variables (array) to avoid using lots of method parameters. It works as I expected but is that a good practice? Actually I wouldn't expect that worked, but I guess class methods are not working as static methods in other languages. class DummyClass def self.dummy_method1 @arr = [] # Play with that array end def self.dummy_method2 # use @arr for something else end end The reason instance variables work on classes in Ruby is that Ruby classes are instances themselves (instances of class Class ). Try it for yourself by inspecting DummyClass

Is there any way to make instance variables "private"(C++ or Java definition) in ruby? In other words I want following code to result in an error. class Base def initialize() @x = 10 end end class Derived < Base def x @x = 20 end end d = Derived.new Josh Lee Like most things in Ruby, instance variables aren't truly "private" and can be accessed by anyone with d.instance_variable_get :@x . Unlike in Java/C++, though, instance variables in Ruby are always private. They are never part of the public API like methods are, since they can only be accessed with that verbose getter. So if there's any