From: "David A. Black" <dblack@...>
Date: 2008-12-06T02:19:32+09:00
Subject: Re: Ruby 1.8.7 Lambas: syntax and scoping issue (are these bugs?

Hi --

On Sat, 6 Dec 2008, Charlton Wang wrote:

> I'm seeing two odd behaviours with using lambdas:

I'm skipping to #2 if that's OK.

> 2. I'm not understanding the scoping rules for lambda with
> instance_evals inside a class:
>
> # If these statements are added at the beginning the
> # the lambda will evaluate them first
> # a = 4  # stmt 1
> # b = 5  # stmt 2
> class Bar
>   attr_accessor :a, :b
>   def initialize
>       @a = 1
>       @b = 2
>   end
>   def foo(&block)
>       instance_eval(&block)
>   end
> end
>
> m = lambda{puts a + b}
> Bar.new.foo(&m)
>
> Without stmt1 and stmt2 above, the code correctly outputs 3. But if
> stmt1 and stmt2 are incommented, the output is 9 which seems to be the
> global scope rather than the scope of the instance of Bar expected
> with instance_eval.
>
> Am I missing something?

When Ruby sees a and b, it favors the interpretation that they are
local variables. If you want to ensure that they're interpreted as
method calls, you can do:

   puts a() + b()


David

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