From: "Hartin, Brian" <Brian.Hartin@...>
Date: 2006-11-11T07:34:25+09:00
Subject: Re: method_missing behaves differently when a method is called via reflection?

Thanks Jacob.  I should have thought of that; it's just like Java
reflection.

-----Original Message-----
From: Jacob Fugal [mailto:lukfugl@gmail.com] 
Sent: Friday, November 10, 2006 4:17 PM
To: ruby-talk ML
Subject: Re: method_missing behaves differently when a method is called
via reflection?

On 11/10/06, Hartin, Brian <Brian.Hartin@pearson.com> wrote:
> For certain methods, it seems to behave differently if called via
> reflection.  Consider the following example:
>
> class Foo
>   def method_missing(method, *args, &block)
>     "#{method} called"
>   end
> end
>
> f = Foo.new
>
> f.bar('a')
>
> -> "bar called"
>
> f.send(:bar, 'a')
>
> -> "bar called"
>
> f.open('a')
>
> -> "open called"
>
> f.send(:open, 'a')
>
> Errno::ENOENT: No such file or directory - a
>         from (irb):8:in `initialize'
>         from (irb):8
>
> ----
>
> I know that 'open' is a Kernel method, but I would have expected
> f.open('a') and f.send(:open, 'a') to behave similarly - either call
the
> Kernel method or call method_missing.  Does anyone know why they're
> different?

All Kernel methods are private. Usually, a Kernel method is called in
procedural style (without a receiver) and since every object includes
Kernel, the private method is visible and called. But when there is an
explicit receiver ("receiver.method_name"), private methods are left
out of the lookup. So when you call f.open, the private Kernel#open is
masked and the unhandled method is passed on to method_missing.
Object#send, however, bypasses privacy restrictions so f.send(:open)
catches hold of Kernel#open and you get the error.

So, in short, it's a matter of: private w/ send vs. private w/o send

Jacob Fugal
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