From: Robert Klemme <shortcutter@...>
Date: 2011-01-19T01:05:48+09:00
Subject: Re: class context

On Tue, Jan 18, 2011 at 4:52 PM, Sebastian Krause <skra@pantolog.de> wrote:
> I thought that the block in the `class_exec`-method would be executed as if
> it appeared within
> a class definition. That seems naive as I discovered the following.
>
> Why does an error occur here?

Because const lookup works statically.  In your example actually
::Const is searched - but not found.

17:03:32 ~$ ruby19 <<CODE
> Const = 666
> class C1; Const = 42; end
> C1.class_eval { p Const }
> CODE
666
17:03:56 ~$

> ----
> irb(main):001:0> RUBY_VERSION
> => "1.9.2"
> irb(main):002:0> class C1; Const = 42; end
> => 42
> irb(main):003:0> class C1; p Const; end
> 42
> => 42
> irb(main):004:0> C1.class_exec { p Const }
> NameError: uninitialized constant Class::Const
>    from (irb):4:in `block in irb_binding'
>    from (irb):4:in `class_exec'
>    from (irb):4
>    from /usr/bin/irb:12:in `<main>'
> irb(main):005:0> C1.class_eval "p Const"       # furthermore this
> 42
> => 42

It's different for non compiled code as you show in the last example.
Here the lookup path is resolved at compile time of the String "p
Const", i.e. not initial compile time of the script.  The string is
compiled inside class_eval.

Kind regards

robert

-- 
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