From: "David A. Black" <dblack@...>
Date: 2007-03-15T05:46:49+09:00
Subject: Re: When introspection doesn't...

Hi --

On 3/14/07, Chad Lester <chad.lester@gmail.com> wrote:
>
> Ruby pop quiz.  How can it be that:
>
>   foo.bar()
>
> is different from:
>
>   foo.method(:bar).call()

Here's one time:

irb(main):001:0> class C; def method_missing(m); puts "caught!"; end; end
=> nil
irb(main):002:0> C.new.x
caught!
=> nil
irb(main):003:0> C.new.method(:x).call
NameError: undefined method `x' for class `C'

> Is it possible to override the "method" method?
> Can you also override the "class" method?

Sure.  I don't think there are any non-overridable methods in Ruby.
It's all open.

> From the FAQ:
> -------------
>
> 7.1 How does Ruby choose which method to invoke?
>
> Ruby binds all messages to methods dynamically. It searches first for
> singleton methods in the receiver, then for methods defined in the
> receiver's own class, and finally for methods defined in the receiver's
> superclasses (including any modules which may have been mixed in). You
> can see the order of searching by displaying Classname.ancestors, which
> shows the ancestor classes and modules of ClassName.
>
> -----------
> If this is true, then I only need to check three places to see what
> method will be called.  Is there a way for me to look the same way Ruby
> does?

You can check the various classes and modules with instance_methods
and other similar methods.

> For those that are curious.... the real life example that raised this
> question for me was in rails.  When you have a Model with a has_many
> relationship it creates an Array-like object that looks very much like
> an Array, but behaves as described above (with a secret undocumented
> deprecated find_all) method.

You sound bitter :-)  Keep in mind that class isn't really very
important in Ruby.  Generally you're more concerned with what a given
object actually does.  So while these AR collections report themselves
as Arrays, the main thing is their behavior, which is kind of a
souped-up Array behavior.


David

-- 
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A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
   (See what readers are saying!  http://www.rubypal.com/r4rrevs.pdf)
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)