From: Rob Sanheim <rsanheim@...>
Date: 2006-09-28T03:44:34+09:00
Subject: Re: Rails for the Rubyist

On 9/27/06, Phrogz <gavin@refinery.com> wrote:
> Paul Lynch wrote:
> > On 26 Sep 2006, at 00:10, Phrogz wrote:
> >
> > > What's the best source for the opposite? Learning Rails for those who
> > > already know Ruby? I'm frustrated by the number of intro tutorials to
> > > rails that have things like "I learned that @foo is called an
> > > 'instance variable'".
> [snip]
> > Agile Web Development with Rails (2nd Ed) is going to be your answer,
> > but I think you'd enjoy Ruby for Rails, too; I know I did.
>
> I just bought the PDF, and I'm not very far into it, but I've already
> found this section:
>
> "In the description of views and controllers, we showed the controller
> setting the
> time to be displayed into an instance variable. The .rhtml file used
> that instance
> variable to substitute in the current time. But the instance data of
> the controller
> object is private to that object. How does ERb get hold of this private
> data to
> use in the template?
>
> The answer is both simple and subtle. Rails does some Ruby magic so
> that
> the instance variables of the controller object are injected into the
> template
> object. As a consequence, the view template can access any instance
> variables
> set in the controller as if they were its own.
>
> Some folks press the point: "just how do these variables get set?"
> These folks
> clearly don't believe in magic. Avoid spending Christmas with them."
>
> Very amusing, but exactly the sort of explanation and attitude that I
> was hoping to avoid. Ah well; certainly other good information in it so
> far. (I'm also discouraged by the appearance that the book takes the
> track of "If you use an RDBMS other than MySQL, it'll mostly work, but
> you're on your own when you run into trouble.")

Regarding this particular magic, I'm pretty sure all Rails does is
loop through all the instace variables on the controller, do a
instance_variable_get to grab it and then an instance_variable_set to
store it on the template object.  So it just uses some the
instance_variable* methods to bypass encapsulation and throw
everything onto the template.

- rob


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