From: balcer <balcersk@...>
Date: 2005-08-22T19:01:18+09:00
Subject: Re: Ruby beginner question 2

Robert Klemme napisał(a):
> Jeff Wood wrote:
> 
>>Alucard wrote:
>>
>>
>>>Hi all!
>>>
>>>I'm using ruby 1.82.  This is the code copy from www.ruby-lang.org,
>>>programming ruby.
>>>
>>>And I found that both the following code cannot run, with the
>>>following error occur:
>>>
>>>song_2.rbw:4:in `initialize': wrong number of arguments (3 for 0)
>>>(ArgumentError)
>>>from song_2.rbw:4:in `new'
>>>from song_2.rbw:4
>>>
>>>So, what is going wrong?
>>>
>>>Thanks in advance!
>>>
>>>CODE:
>>>class Song
>>> def name
>>>   @name
>>> end
>>> def artist
>>>   @artist
>>> end
>>> def duration
>>>   @duration
>>> end
>>>end
>>>aSong = Song.new("Bicylops", "Fleck", 260)
>>>aSong.artist
>>>aSong.name
>>>aSong.duration
>>>
>>>
> 
> #-------------------------------------------------------------------------
> -------------------
> 
>>>class Song
>>> attr_reader :name, :artist, :duration
>>>end
>>>aSong = Song.new("Bicylops", "Fleck", 260)
>>>aSong.artist
>>>aSong.name
>>>aSong.duration
>>>
>>>
>>>
>>>
>>>
>>
>>Your objects have no constructor method ... therefore, it's simply
>>relying on the constructor from Object ( which is implicitly
>>inherited ).
>>
>>So, simply add
>>
>>def initialize( name, artist, duration )
>>@name = name
>>@artist = artist
>>@duration = duration
>>end
>>
>>within either of your class definition examples... then they'll work.
>>
>>The inherited constructor from Object takes no parameters, and that's
>>why you are getting the "initialize wrong number of arguments 3 for
>>0"... You're passing 3 to a no argument constructor...
> 
> 
> A simpler alternative is to just use Struct:
> 
> # direct
> Song = Struct.new :name, :artist, :duration
> 
> class Song
>   # other methods
> end
> 
> Kind regards
> 
>     robert
> 
> 

Sometimes, during the proces of teaching it is not a good idea
to give and alternative :)

Jacek