From: Robert Klemme <shortcutter@...>
Date: 2009-05-03T00:35:02+09:00
Subject: Re: Help me understand 'self' vs current object

On 02.05.2009 17:24, C. Dagnon wrote:
> I'm pretty mystified by this, so I would appreciate any insights...
> This does involve a Rails/ActiveRecord object, but that shouldn't matter
> here, right?
> 
> I'm archiving an object when it gets deleted, so I'm chaining methods in
> a Rails controller:
>         triplet.archive(@user.id).as_delete.save
> 
> But I checked the database and the flag never got reset from false.  I
> added some print statements to as_delete() to get this:
> 
> class ArchiveTriplet < ActiveRecord::Base
>   def as_delete
>     puts "MARKING: #{is_deleted}"
>     is_deleted = true
>     puts "MARKED: #{is_deleted}/#{self.is_deleted}"
>     return self
>   end
> end
> 
> With an additional debug after as_delete() the log shows:
>   MARKING: false
>   MARKED: true/false
>   ARCHIVING: #[ArchiveTriplet..., is_deleted: false, ...]
> 
> What?!
> 
> The easy solution is to change is_deleted everywhere to self.is_deleted,
> but am I misunderstanding what 'self' is supposed to be?  Is there
> another keyword which means what I've been lead to believe 'self' should
> mean?  (ie. 'this' in Java)

You just tripped into the local variable trap.  The very moment you 
placed "is_deleted = true" in that code you told Ruby to allocate a 
local variable which is called "is_deleted" and whose value is "true". 
When you place the explicit receiver "self." before "is_deleted" Ruby 
chooses the method which accesses object state and not the local variable.

http://ruby-doc.org/docs/ProgrammingRuby/html/tut_expressions.html#S3

Kind regards

	robert


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