From: Robert Dober <robert.dober@...>
Date: 2006-06-07T05:46:23+09:00
Subject: Re: Attributes not populated until called?

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On 6/6/06, darren kirby <bulliver@badcomputer.org> wrote:
>
> Hello all,
>
> Pretty much new to Ruby, and I think I am not grasping something
> fundamental
> here. I've written some classes that grab meta tags from various audio
> file
> formats, and overrode 'to_s" to dump the tags to the console, and "to_a"
> to
> dump the tags to an array for use elsewhere in my program.
>
> I am not sure how to explain my problem, so I will just paste in a sessio=
n
> from irb that shows it:
>
> irb> require 'sneetchalizer'  # my class definitions...
> irb> x =3DOggMetaTags.new('/home/music/e/elliottSmith-shootingStar.ogg')


All instance variables are defaulting to nil, none of the instance variable=
s
set in the initializer, are used in to_a, so to_a converts nil to a string
which happens to be an empty string.

=3D> #<OggMetaTags:0xa7cc1ac8 [...rest omitted...]
> irb> x.to_a
> =3D> ["", "", "", "", "", "", ""]
> irb> x.title


=3D> "Shooting Star"


The title  method sets the instance variable @title, therefore to_a  yields
...


irb> x.to_a
> =3D> ["Shooting Star", "", "", "", "", "", ""]


idem

irb> x.artist
> =3D> "Elliott Smith"
> irb> x.to_a
> =3D> ["Shooting Star", "Elliott Smith", "", "", "", "", ""]
>
> So you can see I need to explicitly call each attribute before my array
> gets
> the value. How can I change this so the array is populated automatically
> when
> called?



Here is the class:
>
> class OggMetaTags < MetaTags
>   def initialize(filename)
>     @filename =3D filename
>     require 'ogginfo'
>     @tags =3D OggInfo.new(@filename)
>   end
>   def title
>     @title =3D @tags.tag['title']
>   end
>   def artist
>     @artist =3D @tags.tag['artist']
>   end
>   def album
>     @album =3D @tags.tag['album']
>   end
>   def genre
>     @genre =3D @tags.tag['genre']
>   end
>   def year
>     @year =3D @tags.tag['date']
>   end
>   def comment
>     @comment =3D super
>   end
>   def tracknum
>     @tracknum =3D @tags.tag['tracknumber']
>   end
>
>   def to_a
>     ["#@title", "#@artist", "#@album", "#@genre", "#@year", "#@comment",
> "#@tracknum"]
>   end
> end
>
> If you need more info or want to see all the code please just ask. Thanks
> for
> consideration,


No the programmatic behavior is clear, I fail to see the reason though, but
there might be one.
As a matter of fact there is a good reason to cache the value of the
attribute in the reader but that would be done like this
@year =3D @tags.tag['date']


-d
> --
> darren kirby :: Part of the problem since 1976 :: http://badcomputer.org
> "...the number of UNIX installations has grown to 10, with more
> expected..."
> - Dennis Ritchie and Ken Thompson, June 1972
>
>
>


--=20
Deux choses sont infinies : l'univers et la b=EAtise humaine ; en ce qui
concerne l'univers, je n'en ai pas acquis la certitude absolue.

- Albert Einstein

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