[ruby-talk:5486] Re: Some newbye question

[e-mail] (Yukihiro Matsumoto) writes:

> Hi,
> 
> In message "[ruby-talk:5483] Re: Some newbye question"
>     on 00/10/13, Davide Marchignoli <[e-mail]> writes:
> 
> |>    def example
> |>      a = 99
> |>      return proc { |n| n + a }
> |>    end
> |> 
> |>    x = example
> |>    x.call(2)    # => 101
> 
> |My question was about variable n, the block does not necessarly introduces
> |a fresh variable, instead it (possibly) binds it to an already existing
> |variable. IMHO this treatement of variables occurring as argument of
> |blocks is unrelated to the creation of closures.
> 
> It is necessary.  For example
> 
>   fact = proc{|n|
>     n == 0 ? 1 : fact.call(n-1)*n
>   }
>   p fact.call(4)
> 
> would return 0 if the block does not introduce a new scope.
> But I still want to remove the stumble stone like:

But turning this around, I think the question was why do block
parameters inherit variables from the surrounding scope:

   a = 1
   proc { |a| a = 99 } .call
   a		# => 99

Is there a reason why procs should behave differently to methods here?

   a = 1
   def fred(a)
     a = 99
   end
   fred(12)
   a            # => 1


Dave