From: Robert Klemme <bob.news@...>
Date: 2005-08-22T17:31:22+09:00
Subject: Re: Ruby beginner question 2

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