Rails - Apr 2007 - Is there something I am missing?

this s more of a syntax question then a problem persay. I was optimizing
some older code on one of my projects when I hit and interesting
problem. First the Working Code:

placeholder = 0
while(@record_album[placeholder])
   temp =@record_album[placeholder]
   if(temp.parentid == Parent.id)
     album_tree +="\t<li><a
href=\"\#\">#{@record[placeholder]["name"]}</a></li>\n"
     placeholder+=1
   end
end

Now Non working Code:

placeholder = 0
while(@record_album[placeholder].parentid == Parent.id)
   album_tree +="\t<li><a
href=\"\#\">#{@record_album[placeholder]["name"]}</a></li>\n"
   placeholder+=1
end

The non working code gives me a "You have a nil object when you
didn''t
expect it! The error occurred while evaluating nil.parentid" exception.
I am hoping this is something stupid on my part, but if it isn''t then
why does the error occur

Darushin

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Hi Darushin,

Darushin wrote:
> First the Working Code:
>
> placeholder = 0
> while(@record_album[placeholder])
From Pickaxe, p93, "Ruby has a simple definition of truth.  Any value that 
is not nil or the constant false is true."  The while loop executes until 
@record_album[placeholder] evaluates to nil.
> while(@record_album[placeholder].parentid == Parent.id)
> gives me a "You have a nil object when you didn''t
> expect it! The error occurred while evaluating nil.parentid"
This error occurs because Ruby does not allow you to invoke a method on a 
nil object.  Your working code avoids this by performing the test for a nil 
object prior to attempting to invoke the .parentid method.

hth,
Bill



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Thank you so much. I figured there was a reason for this behavior and
it was driving me nuts to figure out why it was doing this.

Ben

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Hi Ben,

Darushin wrote:
> 
> Thank you so much. I figured there was a reason 
> for this behavior and it was driving me nuts to figure 
> out why it was doing this.
You''re welcome.  Glad to help.

Best regards,
Bill


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> placeholder = 0
> while(@record_album[placeholder])
>    temp =@record_album[placeholder]
>    if(temp.parentid == Parent.id)
>      album_tree +="\t<li><a
>
href=\"\#\">#{@record[placeholder]["name"]}</a></li>\n"
>      placeholder+=1
>    end
> end
Ruby has lots of great iterators which can almost always be used in
place of such iteration schemes using increments:

@record_album.compact.each do |album|
  next unless album.parentid == Parent.id
  do stuff
end

Array#compact will remove any nil entries from your @record_album
array (I assume it''s an array). Note that the behavior of this one
would be different from the original in that the original loop breaks
on the first element that is nil or false and this one will simply
skip it and continue.

Cheers,
Rein


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