From: Gabriel Dragffy <gabe@...>
Date: 2007-08-03T00:30:04+09:00
Subject: Re: Beginner's tutorial and poor attempt at classes


On 2 Aug 2007, at 15:53, Drew Olson wrote:

> Gabriel Dragffy wrote:
>> I still struggling
>> with trying to identify the differences between self.???, @, and @@.
>
> Gabriel -
>
> I'll take a crack at trying to help you with these symbols.
>
> @ - this designates an instance variable within an object. The  
> value of
> this variable differs between instances of the same class.
>
> @@ - this is a class variable. The value of this variable is the same
> between ALL instances of the same class.
>
> self.* - this is used to declare class methods. You call these methods
> directly on a class rather than using a instance of a class.
>
> Below is a little irb session to demonstrate things a bit more:
>
> irb(main):001:0> class Foo
> irb(main):002:1>   def initialize
> irb(main):003:2>     @inst = 0
> irb(main):004:2>     @@cls = 0
> irb(main):005:2>   end
> irb(main):006:1>   def increment_instance
> irb(main):007:2>     @inst += 1
> irb(main):008:2>   end
> irb(main):009:1>   def increment_class
> irb(main):010:2>     @@cls += 1
> irb(main):011:2>   end
> irb(main):012:1>   def print_stats
> irb(main):013:2>     puts "class var: #{@@cls}, instance var: # 
> {@inst}"
> irb(main):014:2>   end
> irb(main):015:1>   def self.say_hello
> irb(main):016:2>     puts "Hello from a class method!"
> irb(main):017:2>   end
> irb(main):018:1> end
> => nil
> irb(main):019:0>
> irb(main):020:0* one_foo = Foo.new
> => #<Foo:0x28d0f34 @inst=0>
> irb(main):021:0> two_foo = Foo.new
> => #<Foo:0x28ced60 @inst=0>
> irb(main):022:0>
> irb(main):023:0* 2.times{ one_foo.increment_instance }
> => 2
> irb(main):024:0> one_foo.increment_class
> => 1
> irb(main):025:0>
> irb(main):026:0* one_foo.print_stats
> class var: 1, instance var: 2
> => nil
> irb(main):027:0>
> irb(main):028:0* two_foo.increment_instance
> => 1
> irb(main):029:0> two_foo.increment_class
> => 2
> irb(main):030:0>
> irb(main):031:0* two_foo.print_stats
> class var: 2, instance var: 1
> => nil
> irb(main):032:0>
> irb(main):033:0* Foo.say_hello
> Hello from a class method!
> => nil
>
> Welcome to ruby! (it's wayyyy better than python :)



WOW! What  a reply! This has got to be the single best thing for Ruby  
- the peeps on this mailing list are awesome!! Very dry, unwelcoming,  
and sometimes rude on the Python list - doesn't apply to everyone on  
there, some peeps are dashing, but the majority...

Anyway. That example does make it somewhat clearer, thank you. I  
think that all in all I do understand what these things are and what  
they do, however, because I haven't come across them before I just  
feel a little unsure when to use them, or even when it's best to use  
them.

Oh one other thing I am liking more about ruby than python is the  
different approaches taken by the languages. I'm starting to have  
warm feelings for Ruby because it's more... human. I can write the  
code using blocks, on one line, or whatever I deem best for that  
particular item. I thought the compulsory white space in Python was  
good, but it makes coding very 'rigid'. Well anyway, enough about  
this Python vs Ruby thing, I obviously don't need to harp on about it  
to the people on this list - you've already settled in the newfoundland!

I'm looking forward to the version of Ruby that gives you a .rbc :)  
then things will be even faster!