From: Robert Dober <robert.dober@...>
Date: 2006-06-07T05:47:38+09:00
Subject: Re: Attributes not populated until called?

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On 6/6/06, Robert Dober <robert.dober@gmail.com> wrote:
>
>
>
> 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
> > session
> > 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
> variables 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 automaticall=
y
> > 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
>

Sorry slipped from a key, continuing...

@year ||=3D @tags.tag['date']
>

which will access the hash only  once.

Hope that helped
Robert

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



--=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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