From: Robert Dober <robert.dober@...>
Date: 2007-07-29T18:11:48+09:00
Subject: Re: how can i use a ruby class in object way

On 7/29/07, Guo Yangguang <gyg22@163.com> wrote:
> Sorry ,i am not show it very clear.Please read this example again:
>
> class Test
> def Test.say_hello
> puts "Hello from #{self.name}"
> puts "hello from #{self.class}"
> end
> say_hello #i don't understand here
ok I see now, well this is "simple" once you have grasped the concept,
but quite difficult before -- as so often ;)

It might be helpful to grasp the concept of self before, I'd advice
Pickaxe for that http://www.ruby-doc.org/docs/ProgrammingRuby/

now in Ruby there is always a self defined, the implicit receiver to
which unqualified messages are sent
Fire up your irb to learn a little bit more about that
536/37 > irb
irb(main):001:0> self
=> main
# This is the default self provided by the Ruby Interpreter
irb(main):002:0> class Test
### look what happens to self when inside a class statement
irb(main):003:1> puts self
irb(main):004:1> end
Test
=> nil
irb(main):005:0> class Test
### say_hello is sent to self, which is Test in this context
irb(main):006:1> say_hello
### but Test does not reply to this message yet
irb(main):007:1> end
NameError: undefined local variable or method `say_hello' for Test:Class
        from (irb):6
        from :0
irb(main):008:0> class Test
### The def statement defines an *instance* method on self, we have therefore
### to write Test.say_hello in order to tell def a method on Test
itself, but you
### seem to know that already :)
irb(main):009:1>   def Test.say_hello
irb(main):010:2>      puts "Hello"
irb(main):011:2>   end
irb(main):012:1> end
=> nil
irb(main):013:0> class Test
### self is set to Test again and now Test responds to the #say_hello message
irb(main):014:1>  say_hello
irb(main):015:1> end
Hello
=> nil
### and just to show that the main object was not influenced by what
we defined for Test
irb(main):020:0> say_hello
NameError: undefined local variable or method `say_hello' for main:Object
        from (irb):20
        from :0
irb(main):021:0>
> end
>
>
>
> Normally,we can use a class anyplaces after defining it ,but in this
> example,i use a classmehod immediately after defining it "in class
> context".This is valid.I means calling a classmethod(not an intance
> method) in a class defintion--not after defining that class--is valid
> .Can you explain it for me? thank you !
Funny but you explained it quite well, if there were no ? I would say
you have made a correct statement. Maybe you are just puzzled by the
dynamic nature of Ruby that everything springs into life when
executed.

class Test
   dosomething
end

as a matter of fact is  equivalent to

Test = Class::new

class Test
  #(1)
   doesomething
end

meaning that at point (1) Test is a well defined complete Ruby class already :)

HTH
Robert
>
>
>
>
>
>
>
>
> Robert Dober wrote:
> > On 7/29/07, Guo Yangguang <gyg22@163.com> wrote:
> >> end
> >> say_hello
> >> end
> >>
> > It is not completely clear what you want to achieve but some remarks
> > might be helpful
> >
> > class Test
> >    def initialize
> >       e="e" # this code is not realy useful, e is a scope local
> > variable that will be thrown away, you probably want to do this:
> >       @e = "e" # this is an instance variable
> >    end
> >
> >    attr_accessor :e  # for some tests below
> >
> >    def Test.say_hello
> >      ...
> >    end
> >    say_hello
> > end
> >
> > Test.say_hello
> > aTest = Test.new
> > puts aTest.e
> > aTest.e = 42
> > puts aTest.e
>
> --
> Posted via http://www.ruby-forum.com/.
>
>


-- 
[...] as simple as possible, but no simpler.
-- Attributed to Albert Einstein